SetSail » Marine Weather

Learning About Expedition Routing – Comparing Weather Models

Steve Dashew — Sun, 27 Apr 2008 05:00:00 +0000

We’ve been using the new (to us) weather routing software to which Troy Bethel introduced us. As cruisers, on an Unsailboat no less, many of the race-oriented features sit idle. But the weather functions are wonderful. This is especially true now that the combination of Sailmail SSB and Iridium are working so well (more on this in a future update). What we like in particular about the Expedition software is that it allows us to easily compare files from different world wide weather models. In some weather patterns one model may be working better than another, and this new flexibility is a huge boost in our ability to understand what is going on, the risk factors, and how to make the fastest and most comfortable passage. If that sounds enthusiastic it is because we are stoked on this product. Lets start with the weather models. Using either Expedition connected to an Internet source such as Iridium, or Sailmail (with the SSB radio or Iridium) the first step is to select a model.

In the image above the green box represents our present position, about 500 miles from Panama. The blue box is the area of the GRIB file we want to request. Notice at the bottom left “NOGAPS” is highlighted. We can either get this once, or subscribe to it in which case it will be sent automatically over a period of days.

Once you hit the “Request” wrench the dialog above pops up. You then choose the time frame (a certain amount of days at various intervals – in this case three days every 12 hours). You can also select the data (wind, pressure at sea level, and 500mb for this model). Finally, control how often the data points are located (here they are on a one degree grid basis). For SSB connections, which can be slow, we try to minimize area and data.

Now comes the cool part. In Expedition you can run a routing with one model at a time, or a combination of models and Expedition will average their data. Here we are going to run the COAMPS, GFS, and NOGAPS together.

The routing is then displayed on the chart with wind barbs that change as you step through the time frame.

You also have this graphical representation, which shows us true wind speed (TWS) and true wind angle (TWA), both of which are key to our progress and comfort. Notice across the top are three tabs. One represents the data for the COAMPS model, the next GFS (for which the data is shown) and finally, the average of the two. For the record, over the last two days GFS and NOGAPS have pretty much agreed with each other, but COAMPS has done the best job of predicting the lumpy uphill conditions of the last 24 hours. We’ll continue to report on this program as we become more familiar with it.

Routing for Cruisers

Steve Dashew — Wed, 16 Apr 2008 00:00:00 +0000

We’re headed for Panama now, and while this route will generally have winds from the aft quadrant, we are using a combination of tools to look ahead and see what the weather gods are planning. Using programs like SailMail, UUPlus, and Ocens we are currently getting used to the new GFS weather model and getting reacquainted with NOGAPS as well. Then there is a new routing tool being developed for cruisers. This is an offshoot of one of the most successful ocean racing programs, Nick White’s “Expedition”. The racers need all sorts of complex calculations with a variety of ways of playing “what if” games. For cruising we want it much simpler and easier to use. That’s one of the things we have been working with Troy Bethel on, an example of which is above. This is a routing, using the performance of Wind Horse, degraded for head winds and head seas and enhanced for downwind acceleration when wind and waves are behind us. The program looks at the projected weather data, and then our performance polar, and calculates how long it will take us for the passage, in this case to Panama from Ensenada, Mexico. As a part of this process the program displays wind data for each segment of the route. Now to the image above. You will note that 25 to 30 knots ate showing coming out of the Gulf of Tehuantepec, and port quarter headwinds approaching this area. These are not pleasant conditions. So, we use the routing software to calculate what would happen if we were to depart a few days later.

Light and variable and from the stern. Much more conducive to marital harmony! While we are using the routing tools to check the wind conditions we are likely to face, Wind Horse is able to maintain her cruising speed up or down wind pretty much regardless of conditions. But in a sailboat you typically need favorable winds to make good progress. By loading the performance polars for your boat into the routing program, the program will tell you how fast you are likely to be – and the optimum course to steer – during each leg of your passage. This is such a powerful tool for getting there quickly that all racing yachts now use some form of routing. It is an even more important tool for shorthanded cruisers. We’ll keep you up-to-date with how Troy’s program development is going with demonstrations of its use over the summer.

Logging Weather Data

Steve Dashew — Tue, 15 Apr 2008 00:00:00 +0000

Those of you who have been with us for a while know we have a passion for and about weather. Weather affects everything we do when cruising: our comfort, passage speed, security. Obviously this applies at anchor as well as on passage. Although the latest generation of weather models are better, they still have problems resolving the data on a micro basis, where it affects all of us. That’s why there are still so many weather-related “surprises” when cruising. Over the years we have worked with various computer folks to develop weather tools. A recent convergence of technology and serendipity has put us in that position again. We are putting our heads together with Troy Bethel, a yachting techie with extensive weather and navigation experience over hundreds of thousands of ocean miles, to adapt a top-end racing program to the needs of cruisers. We get nothing out of this besides friendship, and a chance to have a really cool program for our own use. We’re working with a beta version now and over the next six months we’ll update you on how this is going. If you log the trends for barometric pressure, true wind direction, and true wind speed, you will have most of the information you need to know where your current winds are coming from and what they are likely to do. You can use this data to:

Plan better routes.
Prepare for heavy going, or avoid it.
Know when to heave to and when to proceed.
Stay away from the worst quadrants of a given weather system.
Find better wind strength and angles.
Analyze GRIB and fax to see how accurate it is, and understand if the forecast is going to be late or early.

In short, logging those three items are the key to everything. You can do this in your log book – which is what we usually do. But how much better would it be to have a graphical interface!

How about something like the data above? Barometric pressure, True Wind Direction, True Wind Strength, Speed Over Ground, and Air Temperature.

Having a mean average to smooth out the local oscillations would also be good. That is what the straight line in each set of data represents. The ability to view the graph and mean averages over different time spans is also a help. Is this a short-term wind shift over the last half hour, or is it part of a three- to six-hour trend? This sort of information is is easy and fun to use. We’ve got the processing power now on just about every cruising boat to do this. What has been missing are the sensors, in particular barometric pressure. Well, we are happy to tell you that this problem has been solved. We’ll get into more detail in subsequent articles. For now, know that the system about which we have been dreaming will be available for substantially less than it would cost to replace our lovely old barograph – which is showing the affects of age – and for which parts are no longer available. Stay tuned…

Tongan Volcano Adventure

admin — Wed, 20 Dec 2006 23:00:00 +0000

A SetSailor recently sailed onto the scene of a volcanic eruption near Tonga, where he witnessed the birth of a new island. Fredrik Fransson of Maiken has sent us a gripping account with incredible photos of the experience.

We left Neiafu in the Vava’u group of islands in the northern part of Tonga on Friday the 11th of August, sailing towards Fiji. There was no wind, so we motored along towards an offshore island called Late Island. We had seen on the chart that Metis Shoal and Home Reef in the area were known for volcanic activity. Both are south of Late Island, so we thought it was best to pass it on the north side. Fairly soon we discovered brown grainy streaks in the water. It looked like heavy oil mixed with water. The surrounding water was strangely greenish, like a lagoon, not the deep bluish color that you normally see sailing offshore. The further southwest we got, the streaks turned into heavy bands of floating matter, until the whole horizon was a solid line to what looked like a desert.

So far we didn’t have a problem, since it was such a thin layer on the surface which got pushed away by the bow wave – but when we entered the solid field, it started to pile up, and behaved like wet concrete. The sight was unbelievable; it looked like rolling sand dunes as far as the eye could see. Our speed went from 7 knots down to 1 as the pumice stones dragged along the waterline. I have always been very proud of my Awlgrip paintjob and the fresh bottom job, so my thoughts went immediately to what was happening with that. We turned around as quickly as we could and headed back the same way we came, towards clear water. As we hit clear water, we turned off the engine and cleaned the raw water strainer. The pumice stone floats, so some small pebbles had made it in to the strainer, but mostly they just clogged up the strainer on the outside of the hull. The worst place was the intake to the head, which was packed with the tiny pebbles.

We had no real idea what to do at that point, but we figured out what it must be and that it had to come from a volcanic eruption somewhere near. We joked around about the superstition of not sailing away on a Friday – you don’t get a stronger sign than that the ocean turned to stone! We were too far from land to contact anyone on the VHF radio, so our only options were either to sail south along the pumice rafts, or to head back to the islands. I wanted to make sure that everything was ok with the boat before heading off for a longer passage, so we decided to head back towards land and anchor for the night. The next day we put out a call on the radio with a request for any information about the volcanic eruption, and got an answer that confirmed it, but did not know anything about its whereabouts. We knew that there were two places that have seen volcanic activity in the past, so we decided to sail south of both of them to avoid the pumice rafts that were drifting northwest. We motored out early that morning, heading SSW. We encountered the pumice rafts and sailed along them, until they were so broken up that we could safely drive through them.

We collected a few stones, some a big as a soccer ball – but the bigger they were the more brittle they were, and with the motion of a sailboat they eventually broke into pieces. I am not a scientist, but someone told us that pumice is actually a kind of glass, and when you looked at the bigger pieces, you could really see that structure. Soon we could make out that one of the clouds on the horizon weren’t clouds at all, but actually a smoke stack from the active volcano. The smoke seemed to come from the Home Reef volcanic area. We had been planning to sail south of both these areas, but curiosity overcame us, so we headed toward the southern part of Home Reef.

The closer we came to the island, the clearer the smoke stood out from the surrounding clouds, and every so often a massive black pillar shot upwards toward the sky. You could see particles raining down. Since the wind was pushing the smoke to the northwest, we decided to go in a bit closer. While the sun was going down, we motored up to within 1.5 nautical miles of the island. Later I put the coordinates to be 18deg.59.5S and 174deg.46.3W. It was smoldering with steam, but it was possible to get a good picture of it. You could clearly see the three mounds creating a crater, with one side breaking off, opening up towards the sea. It looked like a big island made of black coal. We reached down and felt the water, and it was warmer, although we didn’t actually measure the temperature difference. Our concern at the time was to sail away from the island before it got too dark, as we didn’t know if we would encounter more pumice rafts. The pumice rafts do not show up on the radar, and since we didn’t know if this was the end of it, we headed SSW toward the southern part of the Lau group in Fiji. It was an amazing experience to witness, although the waterline of Maiken was scratched a bit from all the pumice; I guess that is the price you pay. Since then we have heard of several sailors running into the pumice rafts, some even during the night, which must have been a frightening experience. I think with time the pumice rafts get a bit thinner and easier to penetrate, as we heard of vessels sailing through them, only losing some of their speed. When we were leaving Fiji in the middle of September, we still heard on the radio an account of the pumice drifting up on beaches in Fiji. I got a bit surprised when much later a scientist with the Smithsonian Institute asked for details and photos, and somehow later it ended up with the Associated Press, which led to lots of media coverage. I have been told by another scientist at NASA that sometimes these islands do “disappear” with time, broken down by wind and wave action – but our island still shows up clearly on a satellite photo taken in the middle of October, so who knows.

Indian Ocean Tsunamis – Lessons Learned

Steve Dashew — Mon, 21 Mar 2005 23:00:00 +0000

As awful as the devastation and loss of life has been from the Indian Ocean tsunamis, there are still some lessons that can be learned. The following comments are based on discussions with those on hand, plus previous experiences in California and Hawaii.

Warning Signs

The normal nature of tsunamis is such that they are preceded by a long-range trough. This causes an atypical drop in water level. This occurred during the recent Indian Ocean situation, and was responsible for much of the loss of life at Hilo, Hawaii, many years ago when it was hit (many of those drowned at Hilo were out on the reefs looking for shells in the unusually low tide). If you are anchored in an exposed location, especially if the water is shallow, if the water level drops unexpectedly, head to sea immediately. It will help if the anchor chain is set up to be slipped in an emergency. If ashore, head for high ground.

Ground Tackle

We were surprised to find some boats were held in place by their ground tackle, even inside of the “surf line”. There are photos elsewhere on SetSail showing some boats being held through the first wave. Big anchors, strong chain, a chain stopper, and bow roller structure sufficient to handle the full breaking strength of the chain are part of this system.

Where to Anchor

Anchoring in exposed roadsteads is always a risk. Not so much from tsunamis, but from waves generated by far-off storm systems. Boats have been driven ashore in Cabo San Lucas, the West Indies, and even Fiji by wave systems unexpectedly arriving from storms occurring thousands of miles away. The key to avoiding this problem, and those associated with tsunamis, is sufficient water depth. Required water depth is related to bottom slope, and the shape of the anchorage. Shorelines that funnel wave energy towards the beach require more depth than open shore lines. Bottom shape also has an impact. Deeper is always better.

Atolls

Although there was loss of life on the Indian Ocean atolls, the boats at anchor seemed to fare OK-at least that’s the word we have so far. The water level fell and rose in cycle, but aside from substantial currents, there does not seem to have been significant breaking waves inside of the atolls. We hope to get more information on this in the future.

Marinas

Boats tied up to marinas throughout the affected areas seemed to have not done well. Docks were pulled apart by current, taking the secured boats with them, which were then swirled around in the harbors. Some were driven ashore, others suffered little or no damage. A similar situation occurred in Los Angeles Harbor in the early 1960s as it felt current flux from a tsunami generated by an Alaskan earthquake.

Multiple Wave Cycles

The three wave cycles reported by those on the scene seems to tie to other tsunami experiences. The lesson here is don’t think it is over after the first wave. Reports from cruisers in this event indicate it was the third wave that did the most damage. Here are some additional comments from Al and Beth Liggett, who were on the scene:

Re: the tsunami stuff…Most of it tallies with what we saw or heard from others.

As far as the marina paragraph, we don’t feel that is accurate as the two marinas in Thailand were not affected at all: at Boat Lagoon the water just rose up and receeded. It flooded the hard stand and paint, buckets, shoes, lumber, spinnaker poles and the odd dinghy went whirling about, but the boats at the floating docks were all just fine. Since it is about a 45-minute meander in a narrow, shallow channel, (we can only get in/out on certain tides) leaving is probably not an option. Yacht Haven Marina is situated in a channel that is directly open to the west, and the wave surges did come in under the bridges and rush through the marina. All yachts held without damage. This is the one place that has docks long enough for mega yachts to berth, and we are told that they all had engines on to help hold boat and docks in the currents. This marina regularly has the spring tide rushes of currents coming through it. The management will advise new arrivals to hang off until slack water to make their entrance/exit, and has two “pusher” dinghies to help yachts maneuver into/out of their berths because of the current flow.

There are three marinas in Langkawi, but only two of them were the ones with all the damage; Rebak Marina and Telaga Harbor Marina. They are both very enclosed basins, and the water going in had no place to go except around in whirlpools, thus creating the havoc. The Royal Langkawi Yacht Club had again the rising/falling surge and rushing currents come streaming through. But again, it is open both ends and the waters were able to go in and pass through.

As far as we can gather, the few marinas (small) on the rest of the Malaysian coast had barely noticeable effects. – Al & Beth.

Tsunami Photos Sent by Cruisers

admin — Tue, 18 Jan 2005 23:00:00 +0000

The following photos were taken by Catherine York, who was aboard the J46 Aragorn anchored off Phi Phi Don, Thailand, when the tsunamis hit. These photos cover a one-minute span, showing the first ebb and the first flood.

This is the first of Catherine’s photos of the tsunami. You are looking roughly east. The low part of Koh (Island) Phi Phi Don is to your right. The water is brown in the center from the sand due to the strong suction that comes first with the tsunami. From the position of the four boats on the right, you can see that we had the counter-clockwise rotation of the water on the ebb. The flooding has just begun. The three boats on the left are starting to point toward the entrance to this bay (over your left shoulder). If you look closely, you can see shoreline in the background, unlike the later photos. TAHLEQUAH is the ketch farthest on the right, PAROO is farthest left, NADEMIA is second left.

This is Catherine’s second photo, generally looking at the left side of the last photo. You can see the first crest moving rapidly in and starting to stand up as it reaches shore. David and Sue from PAROO are in their dink, having been aboard ARAGORN, and trying to make their way safely back. Yes, the date is the 25th, because Catherine’s camera was still on Eastern Standard Time.

Catherine’s third photo shows the first crest starting to stand up, behind the two boats. The flood is so strong that NADEMIA and PAROO look like they are moving through the water, although they are still anchored. See below.

This is a close up of NADEMIA from the third photo, moving faster than ever, but see below.

This close-up of PAROO from the third photo shows the greater speed of the wave in the corner of the bay she is in. She was in about 40 feet of water. You can also see how the wave is standing up more against the shore behind her. (Click here for Aragorn’s web site.)

Tsunami at Anchor

admin — Mon, 10 Jan 2005 23:00:00 +0000

Here’s a report from Gavin and Sukey of Scott-Free, circumnavigators who were in Thailand during the tsunamis. Interesting feedback on the three waves and how they behaved in 12m (40 feet) of water.

Hello “out there”. First and foremost, thanks to those of you who have rung or e-mailed over the last few days concerned about our welfare. The situation along the coast here in Thailand, particularly Phuket, is fairly disastrous, as most of you will know, since I understand the coverage has been understandably extensive with some dramatic and horrible images of the mayhem caused by the Tsunamis. I will write about it more fully at a later date but just wanted to get out a “quickie” to say that Scott-Free and her crew are fine as indeed are almost all of our circumnavigating friends. We are not aware of any fatalities amongst the cruising fraternity although there has been some damage to boats (and some have been lost), all of whom were in marinas. The Langkawi Marinas of Rebak and the new one at Telaga were completely destroyed. We are concerned about Ian and Anne on Fidelio who may have been in Galle in Sri Lanka when the waves struck (much bigger waves as well). If you get this, Fidelio, please drop us a quick e-mail. If you have to be anywhere when a Tsunamis approaches the shore, then it is “at sea”!!? (Or on high ground.) We were probably a little bit too close for comfort, anchored as we were in about 12 m. of water about 150 to 200 yards off the beach restaurant at which more than 200 “yachties” had spent Christmas Eve 36 hours previously. In our anchorage (Nai Harn Bay in SW of Phuket Island) we experienced 3 main surges (waves, if you like). The 3rd did the most damage. It was 5 to 6 metres in height and came in, without any warning, at about 1030 am local. It was not a breaking wave, just the water level rising about 20ft in far less than a minute. The Restaurant disappeared under the water and, when the water level started falling again a minute or two later, it retreated sucking everything with it with a huge roaring and crashing. The restaurant had completely gone. Nothing left but a pathetic mess of broken wood and bent metal. Bent and twisted cars had been sucked out of the little car park beside the restaurant and dumped around the beach and on the rocks. The scene on the main beach at the head of the bay was even more devastating. Within minutes, the sea around us was full of debris; the usual beach equipment – sun loungers and mats, tables and chairs from the restaurants, fridges, boats and floats of all shapes and sizes. “Awesome” is a much used word these days. This event was indeed awesome! The yachts meanwhile lifted to the waves. Most would have had 40 to 50 metres of chain out so that took up the surge. The resultant “current” (for want of a better word) ran first into the bay then, a few minute later, out again at 6+ knots which kicked the boats around a bit and a few dragged their anchors, but we never really felt seriously threatened. It was just the most incredible demonstration of the true power of the sea. Anyway, on the law of averages, I don’t think Sukey and I will experience another Tsunamis in our lifetimes!! But…you never know? We were lucky this time! We are fine, but of course the loss of life and livelihoods ashore is truly devastating, not only here of course, but particularly in Indonesia and Sri Lanka, supposedly our next port of call. What to do, eh ?? Having said all that, it is amazing to see the resilience and positive attitude of the Thai people. It is now only two and a half days since it happened and already they (and many visitors and tourists as well) are clearing and re-building. Our little restaurant has already got the framework of a fairly permanent structure in place and the roof goes on tomorrow! He is now hoping to put on a New Years Eve “Party”. We’ll be there! It’s fantastic to see their spirit and attitude. I know this is only one affected area, but I hope a little of this amazingly positive attitude is also reaching the world outside. Thank you for being concerned and I will write again… sometime soon!!! Happy New Year. Let’s hope next year will leave out this sort of disaster, which will, I suspect, when the final death toll is known, go down as one of the worst overall loss of life from a natural disaster in centuries.

2004 Tsunamis: After the Deluge

admin — Mon, 10 Jan 2005 23:00:00 +0000

John Gray runs sea kayak tours based out of Phuket, Thailand. He sent us this article about his experiences with the tsunamis, and his attempts to warn others about the risk thereof.

The tremors began at 7.58am. The long, low-frequency shakes lasted two minutes. It wasn’t the shattering, sharp jolt one expects from a California quake, but it felt ominous. The tremors lasted long enough that I had time to put a bowl of water on the floor to verify the shakes. Sure enough, the water was rippling.

Once the tremors stopped, I mentioned tsunami. Everybody laughed while I talked about the “Big One”. We still knew nothing about the quake and its direction, only that it was a long way off. There hasn’t been a significant tsunami since the volcanic explosion of Krakatoa, Indonesia, in 1883, when perhaps 500,000 people died in coastal villages. I immediately went to the US Geological Service website. Only 15 minutes after the shake, there it was: a temblor that measured 8.3 on the Richter scale off the west coast of Sumatra. This was a Biggie. It grew to 9.0 – massive – and the aftershock was 7.3. The Indian Ocean doesn’t have a warning system, so my next stop was the Pacific Tsunami Warning Centre. Their words were prophetic but typically bureaucratic. An “event” had occurred in the Indian Ocean west of Sumatra but would have no impact upon the Pacific Basin. Thanks for the news, guys. Maybe Australia. This “event” could affect Western Australia. I e-mailed the Australian Bureau of Meterology at exactly 9am: “Any info on this morning’s Sumatra quake and possible tsunami generation?” The response took 24 minutes. Not bad, but not good enough. “We have received an advice from the Tsunami Warning Centre in Hawaii. They opine that a tsunami threat does not exist for the Pacific. However, they do not discount the possibility of a tsunami near the epicentre, which was off the west coast of Northern Sumatra. We have no further information.” A few minutes later, it hit. My response was not as polite: “I read the same advisory from Hawaii. By now you have the news on the devastating tsunami here in Thailand and Southeast Asia. As a 20-year Hawaii resident, I am well acquainted with the Pacific Basin long-range alert system. Now that the barn door is open and hundreds have lost their lives, maybe it’s time for one in the Indian Ocean. Even before I came to Thailand, I was well aware of the Sumatra-Andaman fault-line and its potential for generating tsunamis. It’s time to develop a similar international system for the Indian Ocean. Very frustrating for me to see today’s fatalities – all due to lack of warning and education.” Between e-mails, I called three hotels to watch for receding waters. I was unable to contact any managers, so I called my guide staff together, told them to watch for rapidly receding waters and sent them out to pick up our guests. I told my escort boat captain to move from the pier to deep waters. Reports soon came from Patong and Bang Tao. My Patong transfer guide saw the wave hit. I told him to get over the hill. My Bang Tao transfer guide reported he couldn’t reach the hotel because of the devastation. I reminded everybody to look for receding waters and go to Ao Po, on Phuket’s east coast. I soon got a phone call that waters in Ao Po were dropping fast. My wife told them to evacuate immediately. They got our guests off the pier with grace and speed, and warned the waterfront shopkeepers to run up the hill. Our escort boat shook from the tsunami but survived. Nobody in Ao Po was hurt. If the tsunami wrapped around to the northeast corner of Phuket, it was a biggie. My prediction of hundreds dead immediately changed to thousands. I was surprised that the wave wrapped around Sumatra’s north point with such strength. Sri Lanka and India were in the direct line of fire, but Phuket was a 70-degree turn for any defocused waves. The blessing was that the tsunami was seriously depleted in relation to the full-strength version that hit Sri Lanka. Any low-lying area was in serious trouble. Patong took a strong hit. From the geography it was obvious that the further north the wave went, the stronger it was. Bang Tao simply exploded. Shops behind the hotels had pick-ups in their showrooms. Laguna wasn’t as bad because the beach is a bit higher and the hotels are set back from the beaches (a trend started by environmental planning). At JW Marriott, the alert food and beverages manager was on the beach. He didn’t understand the ocean’s drop, but he did have the presence of mind to evacuate the beach, saving everybody in front of the hotel. Just further north, 30 beach-goers died at a luxury hotel. The worst hit was the fairly new resort of Khao Lak, set right on the beach. The toll will run over 1,000 by the time the clean-up is finished. Phi Phi and Koh Lanta may join Khao Lak in the history books, but it’s too early to tell right now. Points in Krabi are just as susceptible. A survey from Khao Lak to Kata Noi revealed the predictable. Any hotel located 10 metres or more on a cliff, bluff or mountainside escaped devastation. Windows were broken and guests were terrified, but the waters passed below. It was simply the luck of the draw. Millionaires in low-lying beachfront villas were swamped, backpackers in off-the-beach bungalows unaffected. Khao Lak will probably never recover, but Patong can be back in business in a few weeks. Many hotels have cleaned out their lobbies and are ready for check-ins. We ran a sea canoe for 20 people on December 28 – only 40 hours after the tsunami. The bay was calm and beautiful. The next day I was on an overnight trip with people from Hawaii who grew up with tsunamis. We knew the Big One can be devastating and deadly, but once it’s gone, it’s gone. I was amazed at how professional the police, Army and disaster services were. Thousands of Thais performed in a manner that would make the Hawaii Civil Defence system jealous. With no tsunamis for generations, the Indian Ocean basin may have slept through the warning signs, but Thailand can be proud of its reaction to the terrible tragedy. What is over is over. Thailand is not Sri Lanka. Water is clean, rescue and clean-up well organised. Two hundred metres behind the beach, life goes on. The clean-up will last a few weeks. What the Kingdom really needs is for those who loved it the first time around to return and give their support. Knowing Thais, they will welcome them with open arms.

Cruising Weather Sources

Steve Dashew — Mon, 11 Oct 2004 00:00:00 +0000

There is so much weather data available today that capturing and absorbing it can be an overwhelming project. We look for a few good sources that apply to the area in which we are cruising-and then concentrate on those. We start this process with a look at the 500mb data. In areas covered by NOAA fax charts, (North Atlantic and Pacific), 500mb data is broadcast. In most of the rest of the world we use the MaxSea weather “Chopper” to access this data. As the 500mb is a straight output from the computer models, the source is not as important as with surface forecasts. Next, we download surface pressure and wind data. The best source for this is usually the local government forecast. NOAA’s Marine Prediction Center forecasts are excellent, as are those from the UK Met Service, and the Met Services of New Zealand and Australia. We also look to the raw model data from the MaxSea Chopper. Outside the US we’ve found the Oceanic Experimental model to usually have good correlation in the first 48 to 72 hours. Beyond this period, the results can give you a feel for risk factors, but for actual routing, while better than nothing, these have to be viewed with a healthy dose of skepticism. In many areas of the world, the local marine forecasters will issue a discussion of the current forecast, how the different models they use are correlating, and information on the possibility of upgrading or downgrading warnings. Where possible, we always review this data, as it gives us a much better feel for the underlying thinking. It is often possible to call the local marine forecast office and speak to the duty forecaster. Once they’ve finished with the latest forecast, there is often time for a chat. We like to get a feel for what they are looking at which is not in the formal forecast. There will often be risk factors or potential changes that could occur, but for which the forecast process has not yet yielded enough data to enter this into the normal weather message. Speaking with the local weather guys can also yield information on clues to watch for in the government forecasts and our own on-board observations. We put the most emphasis on the data which we can observe on board. Trends in barometric pressure, wind speed and direction, and clouds give a really good feel for what’s coming at us. And if there’s a conflict between what our observations are telling us and the forecast, we normally go with our own observations. In the olden days we noted this data hourly in our log book. Now we use the MaxSea Data Trend Center, which graphically tracks wind direction, speed, and barometric pressure. We also use our radar as a close-in weather tool. We can pick out frontal boundaries, squall lines, and individual squalls at the maximum distance of the radar. On Beowulf this was as much as 50+ miles with the radar display offset. On the new boat, with a more powerful radar, we expect this range to extend out to 70 or 80 miles. The Chopper data is accessed using an e-mail source. We’ve done this with SailMail and our SSB receiver, with Iridium and Globalstar sat phones, and with land lines, when they are available. We particularly like the “subscribe” function, where we can designate what data we want, and then it is automatically sent to our e-mail address each day. The easiest way for us to get government faxes is with a dedicated fax receiver-although you can also pick these up with the SSB radio and a demodulator. When we’ve been in Globalstar Sat Phone range, we’ve sometimes found it helpful to download the NOAA fax charts directly from the web (Iridium is usually too slow for this). The advantage here is timing-we can get the latest chart a couple of hours earlier on the Internet than when it is broadcast via SSB. If we’re crossing the Gulf Stream, that two or three hour head start can make a big difference! Another good source of weather are cruisers reporting in to ham or SSB nets. However, we’ve often found that this information is not in a consistent format. Is the wind direction given in true or magnetic? Are wind speeds true or apparent? And when was the last time the barometer was calibrated? When we hear data which is way off what we would normally expect, we discount it, or ask for a clarification. With Internet or e-mail access it is now possible to get buoy and land-based observations as well. We have not used these in the past, but when we take off cruising on the new boat we will do so-if there is data in the areas that we’re cruising. Over the years we’ve used a number of different routing services. These have usually been for out-of-season voyages through the tropics, where there were hurricane threats to evaluate. We like having someone with whom we can discuss the data in detail, and ask questions which may not have been answered by the forecasts or discussions we’ve received onboard. However, experience has taught us (the hard way) never to relinquish the final decision-making authority to land-based routers. The problem with all of this data is interpreting it. The basics of weather analysis and making the appropriate tactical decisions is pretty simple. But you do have to have an understanding of the fundamentals. When we’ve been ashore or at anchor for a long period of time, we always go back and skim through our notes on weather interpretation and tactics. It all comes back pretty fast, but we don’t want to be scratching our heads with a gale bearing down on us offshore. A final word on this subject. Understanding forecasting and tactics can seem intimidating. From the outside looking in the subject looks complex and difficult to learn. But there are so many resources available today that learning the basics and practicing are easier than they have ever been. Our advice is to put this skill at the top of the to-do list. It will be fun on land, and pay huge dividends once you start to cruise.

Get Background Info on Marine Weather Forecasts

Steve Dashew — Sun, 10 Oct 2004 23:00:00 +0000

We’ve recently discovered a valuable new resource. You can download daily technical discussions from Marine Prediction Center forecasters with the behind-the-scenes thinking that goes into their forecasts.

We’ve had an ongoing conversation about the forecasting process over the years with Dave Feit, who runs the Marine Prediction Center. Recently Dave pointed us to a new (to us) resource, which is a technical discussion of the North Atlantic and Pacific forecasts. This includes how the weather models are behaving, and what various scenarios are for the different forecast products. These “interpretations” are done in a sort of shorthand. These messages were originally developed for dissemination to National Weather Service employees via teletype (50baud!) and so they have a lot of contracted words (acronyms). For the most part, these are words where the vowels have been omitted, and after you’ve read a few, they will start to make sense. For example “dcrsg” = “decreasing”, an “cdfnt” = “cold front”. Some other acronyms often used are: ASCD = associated ATTM = at the moment ETA = Eta model CAA = cold air advection HPC = Hydrometeorological Prediction Center If you read through a couple of messages, and at the same time watch the various surface and upper level faxes, you will begin to get a feel for what the forecasters in the Marine Prediction Center are watching. This is valuable now, before you go, as a learning experience. And it’s incredibly useful just before you head offshore. At the top of the Marine Prediction Center Forecast Products page you’ll see links for Atlantic Forecast Discussion and and Pacific Forecast Discussion , as well as Gulf, Caribbean, and DSW Atlantic Forecast Discussion .

When you click on one of these, a file will download which you can then open and read in your word processor. (We open ours in Microsoft Word). You will also find on this page various text forecasts which are broadcast on ssb, vhf, and via fax. Following is an example of a recent Marine Interpretation Message for the Atlantic: MARINE INTERPRETATION MESSAGE NATIONAL WEATHER SERVICE WASHINGTON DC MARINE PREDICTION CENTER/MARINE FORECAST BRANCH 0116 AM EDT Oct 18 2001 FORECAST DISCUSSION: MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT WEATHER FOR NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N: Ref. AWIPS…Surface/NCEP Graphics/Surface Obs/WATL wind/wave. COLD POCKET MAKING WAY ACRS NEW ENGLAND AND NRN WATERS WITH 44025 29 KT G 35…BUZM3…38 KT G 44 KT AT 03Z. SEAS HAVE CONTINUED TO NOSE UP TO 13 FT AT 44011…A LTL AHEAD OF WAVEWATCH. CONSIDERING EXTENDING GALE WARNING INTO MORNING HOURS GULF OF MAINE AND GEORGES BANK…WILL MAKE FINAL DECISION S OF NEW ENGLAND AS WHETHER TO HAVE GALE FOR REMAINDER OF NIGHT OR A BRIEF PORTION OF MORNING. SOME MINOR DIFFERENCES SHORT TERM AS PER AVN AND ETA WITH BIT OF A SURGE EARLY THIS MORNING ACRS THE NORTHERN CANYONS TO HATTERAS CANYON AS HIGH BUILDS OUT. AVN A TAD STRONGER THIS RUN WITH ETA CONSISTENT WITH 18Z RUN. CURRENT FCST HAS THIS HANDLED AND WILL LEAVE AS IS…MAY CONSIDER A REMAINDER OF NIGHT FOR HUDSON TO HATTERAS CANYON. NE FLOW S OF HATTERAS…AS HI BRIDGES OUT OFF DELMARVA GRADIENT TO TIGHTEN S OF HATTERAS LATER TONIGHT. CURRENTLY WINDS HAVE BEGUN TO NOSE UP A BIT AS SHIFT TO N THEN NE…WILL CONT WITH CURRENT WORDING AND BRING WINDS UP TO 15 TO 25 KT WITH A SPLIT OF CAPE ROMAIN FOR SEAS THROUGH FRI WITH 7 TO 10 FT. EXTENDED…NO BIG DIFFERENCE WITH EXITING TROF 60 TO 66 HRS. TREND HAS BEEN WEAKER AS TROF LOSES AMP. AVN HAS SETTLED INTO A FRAGMENTED DVLPMNT TO LIFT NE FM OFF SE COAST FRI NIGHT INTO SAT. CANADIAN REMAINS STRONGER WITH LEAD IMPULSE AND WITH SECONDARY TRAILG LOW. AM NOT CONVINCED THIS THE CASE. ECMWF IS FASTER AND WEAKER…EARLIER UKMET IS ALSO FRAGMENTED. WILL CONSIDER BACKING OFF ON CURRENT WORDING FOR PSBL GALES S/E 1000 FMS AND MODERATE WINDS NEW ENGLAND WATERS. WARNINGS…NT1 NEW ENGLD WTRS…GALE…GULF OF MAINE AND GEORGES BANK FOR EARLY MORNING…S OF NEW ENGLAND REMAINDER OF NIGHT. NT2 MID ATLC WTRS…GALE…NTHRN PORTION OF S/E OF 1000 FMS. FORECASTER SIENKIEWICZ. MARINE FORECAST BRANCH