SetSail » Weather

Tropical To Extra Tropical Storm Development – The Most Dangerous Weather Pattern

Steve Dashew — Sat, 17 Sep 2011 15:02:16 +0000

We have mentioned in the past that while hurricanes get the press, their area at sea is limited and they are relatively easy to avoid. If the tropical system morphs into an extra tropical configuration, it covers a huge area, and is nearly impossible to get away from. We have a perfect example of this right now. If you go to http://www.opc.ncep.Nola.gov/shtml/A_brief.shtml you will find the most recent complete weather fax run from the Marine Prediction Center in the USA. The surface weather analysis shown above represents the remnants of tropical storm Maria, centered between Newfoundland and Greenland. It is orders of magnitude larger than Maria was, and has moved at speed of 40 to 50 knots over the last 24 hours. You would not want to be caught unawares by one of these systems. There is lots more on this subject in Mariner’s Weather Handbook.

Dvorak Technique Study Manual

Steve Dashew — Mon, 08 Nov 2004 05:00:00 +0000

Dear Madam, Sir, Two years ago, I ordered your Mariners Weather Book and read it. A compliment to your book. It is one of the best books, to learn maritime weather by sailors. On page 366, you refer about the Dvorak Technique to understand hurricane forecasting. Please give me the detailed information about this book: Where can I order it? What’s the price? Yours sincerely, A. Schroeder

Howdy: The Dvorak Technique manual used to be available from NOAA in the U.S. However, it is no longer in print. We are exploring a means of bringing this data to our readers, but have so far not yet found a solution. Regards–Steve Dashew

World Storm Patterns

Steve Dashew — Sun, 04 Nov 2001 05:00:00 +0000

Hi, I am enjoying reading our book “Surviving the Storm”. I know you could not cover all the topics, and I have not read the whole book yet, but I could not find data or reference to world storm patterns. If one was chicken, and wanted to avoid category two and three heavy weather storms (page 16), what cruising routes could be planned, and where not to be at what time of year? I recall some published charts that show wind direction and speed at various locations. What about information on routes and the best time of the year to avoid bad storms. Could you name a few good sources for me. I get the hint that New Zealand is risky at best. If I missed this information in your book, please let me know where it is located. Thanks, Mike

Hi Mike: There are no hard and fast rules about avoiding storm seasons and/or areas. The weather varies too much from year to year. The pilot charts and sailing directions will give you a general idea for planning, but you need to check out the pattern in the time period in which you are sailing.

You can do this by talking with local forecasters during the time frame you are getting ready to leave, or with some of the commercial routers who are also in this business. Or, get up to speed on the weather forecasting process yourself and keep an eye on what’s happening on the internet for a couple of months before it is time to take off.

Check out the weather links on SetSail–they are a good start. Regards–Steve

Unusual Revolving Storms

Steve Dashew — Mon, 03 Jul 2000 05:00:00 +0000

Firstly, let me say how much I am enjoying your books, Mariner’s Weather Handbook and Surviving the Storm. For anyone with the slightest interest in the weather around them and in taking a boat to sea, they are excellent reading. However, I do have a couple of queries:

On page 340 of the ‘Mariner’s Weather Handbook’ you show three photographs of tropical revolving storms, when and where they should not be, one off Angola (West Africa) in April 1991 and two of one storm in the Eastern Mediterranean in January (no year mentioned). It is my understanding that no tropical revolving storms have ever been reported in the South Atlantic (until now) and that the sea temperatures in the Eastern Mediterranean in January are certainly not high enough for cyclogenesis nor is the ITCZ anywhere near the Mediterranean. Have you any explanation for these phenomena and/or a year for the Mediterranean storm (I would like to research past meteorological records to find what conditions actually existed in the latter case).

I look forward to your reply, Brent

Hi Brent: The pro’s tell me that part of the reason there have never been any tropical storms in the S. Atlantic is that there’s rarely anyone down there to report them. The point we were trying to make is that ANYTHING can happen with the weather–so, be prepared.

To get the cyclogenis cooking you all you need are a bunch of thunderstorms,and a quiet upper atmosphere to allow the T-Storms to cook. Once they begin to rotate…

As for the series in the Med–while the satellite images appear to confirm cyclogenisis, the storm actually developed over Africa where it might have been warm enough to start the initial development, they could also be an indication of a bent back warm front structure.

As we are cruising right now I don’t have my notes, so I can’t give you any pointers are where to get more data. Regards–Steve

Avoiding Bad Weather – Predicting the Track of a Low Pressure System

Steve Dashew — Tue, 30 Nov 1999 05:00:00 +0000

Dear Steve, I have just read your analysis of the Queens Birthday Storm 1994. First of all, I’d like to thank you for your efforts in producing such detailed analysis – they are a wonderful education for relative novices like myself. I do have a question you may be able to help me with.

I agree with your position that the best way to avoid bad weather is to get out of the way – by staying in shelter or sailing fast in a direction which avoids the storm track.

Avoiding the storm track has to rely on knowing which way the storm/low pressure system is likely to be moving. These days, with all the communication aids to obtaining recent surface charts obviously has made this vastly easier than it was 10 or 20 years ago.

However there may well be occasions when you have lost communication and you know, either from before your weather fax went down, or from increasing wind and the barometer going down, that there is potential for bad weather.

You can simply find in which direction the low lies and work out the quadrant you are in.

However, my question is, how reliably can you estimate the potential storm track if you are no longer getting comms? The latitude you are sailing in and in which ocean obviously has a strong bearing as most lows are likely to track NE, E or SE if you are below 25/30 degrees South. Is this true, or can you be more accurate than NE/E/SE, and how?

Cyclones can and do seem to go W – possibly more frequently than they track NE/E/SE? Why is this? And will tropical lows do the same?

There is probably a lot more to this than I realize, but I would be greatly interested in any comments you might have and how if possible can you predict the track.

Best regards, Peter P.S. I have purchased Practical Seamanship – love it, so also just ordered the Cruising Encyclopedia.

Hi Peter: Good question! First, the forecasts and faxes are usually a good indicator of general weather. But often the details on timing, location, and intensity will be off. So your off-the-boat sources need to be confirmed with onboard reality, and if there is a difference, appropriate adjustments made to tactics.

If all outside sources are down, you still have a pretty good idea of what is going on by logging barometric pressure, wind direction and velocity, waves, and cloud type/direction. The trends in this data will usually enable you to forecast the low center and where you are in relation to it.

There are usually trends in how systems behave in various parts of the world, and these can be used to help figure out what is going on. But sometimes weather systems behave differently than the norm. So, you need to be alert to variations.

Tropical lows are usually steered by upper level winds. However, while there are sometimes patterns to how this occurs, there are plenty of atypical situations too.

Our preference is to reduce risk factors by choosing the best season to travel, and avoid being bound by schedules. Taking this approach, together with getting the passage over with as quickly as possible, substantially reduces weather risks. Keep in mind that prior to the last 20 years, very little accurate offshore weather data was available. Regards – Steve

Sea Breeze Effects

Steve Dashew — Tue, 30 Nov 1999 05:00:00 +0000

Steve, My question relates to how the sea and land temperatures influence wind patterns. If the sea temperature is warmer than the adjacent land, then what type of flow can I expect? This specifically relates to So. Calif. waters and down towards Ensenada. Thanks, John

Hi John: There is a direct relationship between sea and land temperatures. At its simplest, warm air over the land rises, and the cooler air from over the adjacent ocean fills the vacuum created by the rising warm air. This is known as a sea breeze affect.

At night the process often reverses, with the cooler land air descending and flowing out over the now warmer ocean.

So, in S. California and along the Baja coast this is why you get an afternoon onshore (sea breeze) flow – which often reverses some time after midnight through the early morning hours.

To the extent that there is a pressure gradient present exclusive of the temperature differential, the sea breeze or night time land breeze, will reinforce the gradient or reduce it.

There is an entire section in our Mariner’s Weather Handbook which goes into this in great detail.

Steve

PS-differentials in sea temperature, especially in areas like the Gulf Stream or South Australian current also have a big impact on local weather.

South Pacific Typhoon Season

Steve Dashew — Tue, 30 Nov 1999 05:00:00 +0000

Hi folks – If you were a small Falmouth Cutter 22, heading around the world, on what date would you most like to leave Panama, in order to best avoid the South Pacific typhoon season? This is the only piece of essential cruising information I can’t find on your marvelous web site. Thank you very much. Dr. Gene

Hi Gene: Not an easy question to answer as it depends on el Niño, and how fast you move with your boat. Generally speaking, El Niño years tend to be more active in the eastern tropical South Pacific – which means the Tuomotus and Societies for sure and sometimes the edges of the Marquesas.

The "season" is the opposite of the N. Hemisphere – so you start to get nervous by mid-October and keep a close eye on things. The slower the boat, the closer the eye.

On the other hand, leaving from Panama, through the Galapagos, and onto the northern Marquesas Islands is usually considered cyclone free.

So, when you leave Panama depends on how fast you push at sea, and how much time you want to spend enroute. In a non El Niño year I would be happy organizing my schedule so as to leave from the Marquesas by late March or early April. If El Nino is brewing, I’d push this back a month or six weeks.

But you have to watch the weather patterns carefully for anomalies- much easier to track these days with all the satellites and communications.

All of this is covered in great detail in our Mariner’s Weather Handbook. Regards – Steve

Sailing North From Mexico

Steve Dashew — Tue, 30 Nov 1999 05:00:00 +0000

Our catamaran is being delivered to Ensenada just after Christmas. Can you point me to information regarding sailing north from Ensenada to San Francisco. Thanks, Steve

Hi Steve: Check out the weather links on SetSail.com for the Marine Prediction Center and their faxes. In general, you want to head N ahead of and with fronts–as the wind will be behind you. Or, wait until a high pressure system has established itself after the front and then power. Lots more details on how to do this in our Mariner’s Weather Handbook. Regards–Steve Dashew

Weather Help for 1st-Time Participants of Rallies

Steve Dashew — Tue, 30 Nov 1999 05:00:00 +0000

I would like to see information for first time participants on rallies, races and regattas. I went on the NARC Rally thinking it was about safety and found myself in 30-35 kt. winds with gusts even higher. There was no reliable weather information after the weather briefing in Newport and trusted the coordinator to keep us safe and informed. We ended up calling the weather coordinator on our Gobalstar because he had no way of keeping updated on the weather. I would like to know what questions I should ask IF I EVER DO THAT AGAIN. What I should look for in a coordinator to judge the safety of the operation.

Hi There: Your question got passed to me.

First, you need to be responsible for your own weather decisions. This is critical. No weather router can make those decisions. They can advise, but the models are often off a bit on their timing, and none of them are very good on a micro basis–what is happening on your own patch of ocean. Then there is the issue of what the boat and crew are capable of handling.

Understanding weather, and the best tactics associated with it should be everyone’s first priority on the learning curve. This is ahead of anything to do with equipping the boat, or any other aspect of seamanship.

And it is not that hard. There is some study involved, you might want to spend some time taking a class, and you will need to practice at home (but that’s fun). With the internet, and some of the software now available, you can practice based on the current data, and then check out how your forecast is stacking up the next day. Regards–Steve

Wx Analysis for Caribbean to East Coast US Passage

Steve Dashew — Tue, 30 Nov 1999 05:00:00 +0000

Re sailing to Bermuda, what’s the best weatherfax station for the trip–New Orleans? And for Bermuda–Newport, is it the Boston station? Anything we need to worry about weatherwise for the Virgin Gorda–Bermuda run or is it pretty straightforward this time of year? As for Bermuda–Newport, I am basically terrified and am quite tempted by American Airlines. This, from someone who’s sailed 5800 miles, now! There’s no reforming a worrier…

Hi Candace: Radio stations first–use both New Orleans and Boston from the Caribbean up, and start watching them two to three weeks ahead of time to get a feel for the weather patterns.

You will want to keep an eye on the 500mb charts from Boston right from the beginning–to keep an eye on the risk factors (re-read the risk factor stuff in Mariner’s Weather Handbook, and pay particular attention the 500mb stuff). The 500mb troughs occasionally “dig” south and pick up moisture/energy from the sub-tropics–which can then affect you south of Bermuda.

The trip to Bermuda from the Islands is easier and has less to be concerned about, but the weather can still be unpleasant. So, keep your eyes open, and then push really hard to get the passage to Bermuda over as quickly as possible.

Bermuda to the East Coast is a question of how the season is shaping up. Don’t be in a rush. Wait for the right conditions. This could mean hanging out in Bermuda for two or three weeks, if there is a cut off low messing things up–as it did last May. The fronts will be coming through in a pattern. Try to avoid frontal stuff in the Gulf Stream. It is often better to heave to on the Bermuda side and wait for a front to pass over the GS, then meet it mid-way.

You might want to try using a routing service like Commander’s on both legs. And if you have MaxSea Routing on board start running practice routings now, to get a feel for what they are showing with the current “grib” files.

And don’t worry about worrying–it is a healthy response to the sea and weather, and will keep you out of trouble (I still worry about weather!). Steve