We’re almost half way through our passage to Panama, about ten hours from Acapulco, Mexico. The two of us are back in the rhythm of long distance voyaging, getting our sleep at odd times, and enjoying being at sea.
With Acapulco close by we are thinking of pulling in for the evening. There are two advantages to stopping. First, this allows us to give the engine room a thorough check after five days of continuous powering. Second, the price of diesel fuel in Mexico is controlled by Pemex, so we are probably going to find the same inexpensive price as in Ensenada (about US$2.40 per gallon).
Negatives involve the work of stopping (getting fenders and dock lines ready), the paperwork hassle (OK, we’ll have the marina do this but it still kills half a day) and most important, breaking our seagoing rhythm.
The bigger issue is weather in the Gulfs of Tehuantepec and Papagayo. We would not mind a real blow on the beam or stern quarter to get some video footage. What we do not want are winds on the bow quarter which are hard on fuel burn and motion.
You can look at the fax charts, which we do of course, but they only give a rough idea of what is going to happen, and it is hard to predict where you will be in each time frame. So what we are doing now is using a new routing tool, previously discussed, which looks at the raw GRIB weather data (and so is less accurate than a fax with human interpretation), and then takes the performance of the boat in various wind strengths and angles to calculate how fast you will go and where you will be when. Under sail this helps to chose the optimal route to play the weather. For Wind Horse, which goes almost the same speed regardless of conditions, it helps us decide if we want to go or stay for a day in Acapulco.
Here is the stretch of Central America we are at present traversing. We are at the left hand side of the image. The wind barbs represent the conditions starting tomorrow, assuming we stop for the evening.
This is the bottom half of the routing data. Note the TWS and TWA data. Winds are light or on the beam for all but the last day which is heading into Panama where it is always on the nose as you begin to feel the Caribbean trade winds.
Finally, a close up of the Gulf of Tehuantepec with our position a third of the way across (tiny red dot).
We looked at the same data based on not stopping and it is slightly less favorable, so stop we shall.
We are watching the text forecasts along with the weather faxes for the area. But as stated earlier, these do not give much data. Of far more interest is the duty forecaster’s discussion of the forecast itself, model and other data being used, and what they think might be going to happen. NOAA posts these for each region; you just have to search for them (the major ones are a part of the Sailmail "Saildocs" system). We have appended the latest info below. While somewhat technical, if you do a little homework these quickly become amongst the most valuable of weather tools.
URL: http://weather.noaa.gov/pub/data/hurricane_products/eastern_pacific/weather/discussion.txt Date: 20 Apr 2008 13:05:14 -0000
Last-Modified: 20 APR 2008 09:31:30 -0000
Expires:No;;899500AXPZ20 KNHC 200931 TWDEP
TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SUN APR 20 2008 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM
THE EQUATOR TO 32N…EAST OF 140W. BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0900 UTC. ..ITCZ…
ITCZ AXIS IS CENTERED ALONG AXIS 07N77W TO 04N84W TO 04N103W TO 06N112W TO 03N140W. SCATTERED MODERATE TO ISOLATED STRONG
CONVECTION WITHIN 240 NM N OF AXIS BETWEEN 112W AND 116W. SCATTERED MODERATE CONVECTION ALSO WITHIN 30 NM OF COLOMBIAN
COAST S OF 5N. SCATTERED MODERATE CONVECTION FROM 7N TO 9N BETWEEN 95W AND 100W. SCATTERED MODERATE CONVECTION FROM 7N TO
9N BETWEEN 125W AND 127W. ..DISCUSSION…
E OF 110W…A 01Z HIGH RESOLUTION QUIKSCAT PASS SHOWED 25 TO 30 KT NORTH FLOW THROUGH THE GULF OF TEHUANTEPEC. THE 30 KT IS
SOMEWHAT SUSPECT SINCE THE DATA WERE ON THE EDGE OF THE SWATH…BUT 25 KT FLOW IS PLAUSIBLE. THESE WINDS ARE DUE TO
STRONG NLY FORCING THROUGH THE BAY OF CAMPECHE TO THE NORTH…AND SHOULD ABATE THROUGH MIDDAY TODAY. FURTHER S…A
2330Z QUIKSCAT PASS SHOWS 20 KT ONGOING THROUGH THE GULF OF PAPAGAYO…IN RESPONSE TO STRONG TRADE WINDS OVER THE CARIBBEAN.
THIS WILL LIKELY PERSIST OFF AN ON THROUGH 48 HOURS. ALOFT…A MID/UPPER RIDGE CONTINUES IN PLACE OVER SOUTHERN MEXICO. RELATED
SUBSIDENCE IS KEEPING MUCH OF THE CENTRAL AMERICAN AND MEXICAN COAST ALMOST CLOUD FREE FROM NICARAGUA TO MAZATLAN. AN UPPER
TROUGH ORIENTED E-W EXTENDS FROM 80W TO 110W SOUTH OF THE MID TO UPPER RIDGE. DIVERGENCE ALOFT BETWEEN THE TROUGH AND RIDGE IS
ENHANCING CONVECTION OFF THE COLOMBIAN COAST AND ALONG AND NEAR THE ITCZ AS NOTED ABOVE. GFS AND EURO GLOBAL MODELS SHOW THE
UPPER CYCLONIC TURNING PERSISTING THROUGH MONDAY…AND THE GFS HINTS OF UPPER DIVERGENCE TO THE EAST SUPPORTING AT LEAST MODEST
CONVECTION ALONG THE ITCZ BETWEEN 90W AND 100W THROUGH 48 HOURS. W OF 110W…A MID LEVEL SHORT WAVE TROUGH N OF 24N ALONG ROUGHLY
120W IS PUSHING WESTWARD TOWARD THE NORTHERN BAJA COAST…AWAY FROM A STATIONARY CUT OFF LOW NEAR 23N142W…NE OF HAWAII BROAD
AN UPPER RIDGE TO THE NORTH OF THE CUT OFF LOW IS FLATTENING OUT AND SHIFTING SE AHEAD OF A DEEP TROUGH DIGGING TO THE NORTH OF
HAWAII. AS THE THE RIDGE SHIFTS SE THROUGH THE NEXT 48 HOURS…THE CUT OFF LOW WILL OPEN UP AND LIFT OUT TO THE NE. A
1034 MB SURFACE HIGH SHIFTS SWD ALONG WITH THE UPPER RIDGING THROUGH MON. THIS WILL MAINTAIN FRESH NLY FLOW OFF THE BAJA
COAST…ACCOMPANIED BY NLY SWELL TO 12 FT. IN ADDITION…FRESH TO STRONG TRADES S OF THE RIDGE WILL PERSIST GENERALLY W OF
125W. FURTHER SOUTH…CONVECTION CONTINUES TO FLARE NEAR 115W WHERE A SURFACE TROUGH INTERSECTS THE ITCZ. THE TROUGH AND
RELATED CONVECTION WILL CONTINUE SLOWLY W THROUGH 48 HOURS REACHING 130W…WITH SOME ENHANCEMENT FROM DIVERGENT FLOW ALOFT.