Caribbean (Leeward Islands) Weather Basics

Morning squalls rolling down Drake Passage

Sailor’s geek out about many of the aspects of sailing and the sea – we love to learn. Weather, among all the things we learn and do while sailing, is easily the beating heart and the breath of a life under sail.

While we are underway we are “keeping a good weather eye out” for squalls. Easy to see coming, these are short lived blows that once spotted we have a good 5 to 15 minutes to shorten or drop sail and shoulder through them.

Longer range forecasts can inform us of approaching troughs, depressions, or more significant weather systems coming across the southern Atlantic toward the islands. Continue reading below to learn more about what we talk about, when we “talk about the weather”…

“Fair winds and a following sea to you all in the meanwhile.”

Here’s the forecast for the Leeward Islands as of this post today:

Southwest Tropical North Atlantic and Caribbean Sea (OFFNT3)
000
FZNT23 KNHC 290900
OFFNT3

Offshore Waters Forecast for the SW and Tropical N Atlantic and
Caribbean Sea
NWS National Hurricane Center Miami, FL
400 AM EST Wed Nov 29 2017

Offshore Waters Forecast for the Tropical N Atlantic from 07N to
22N between 55W and 64W, the SW N Atlantic S of 31N W of 65W
including Bahamas, and the Caribbean Sea.

Seas given as significant wave height, which is the average
height of the highest 1/3 of the waves. Individual waves may be
more than twice the significant wave height.AMZ025-292100-

Offshore Waters Leeward Islands-
400 AM EST Wed Nov 29 2017

.TODAY...E winds 10 to 15 kt. Seas 4 to 6 ft. 
.TONIGHT...NE to E winds 10 to 15 kt. Seas 4 to 6 ft. 
.THU...E winds 5 to 10 kt. Seas 3 to 5 ft. 
.THU NIGHT...E winds 5 to 10 kt. Seas 3 to 5 ft. 
.FRI...E to SE winds 5 to 10 kt. Seas 3 to 5 ft. 
.FRI NIGHT...E winds 5 to 10 kt. Seas 3 to 5 ft. 
.SAT...NE to E winds 5 to 10 kt. Seas 3 to 5 ft. 
.SAT NIGHT...NE to E winds 5 to 10 kt. Seas 3 to 5 ft. 
.SUN...NE to E winds 10 to 15 kt. Seas 3 to 5 ft. 
.SUN NIGHT...NE to E winds 10 to 15 kt. Seas 3 to 5 ft. 

In General

  • Predominant Trade Winds: NE / E / SE at 10-25Kts.
  • Year round temperatures range: 78° F (25°C) to 85° F (29° C).
  • Dry Season: February – June:
    • occasional small showers.
  • Wet Season: July – January:
    • More frequent showers.
    • Occasional rainy days:
      • With Squalls: can be 40kts +.
      • Seen from afar.
      • Can’t gauge wind – assume a lot.
    • Infrequently squalls or cold fronts can produce Westerly winds making usual anchorages uncomfortable.

Winter Months

  • Storms and cold fronts further north create “Northerly Swells”

(Like wind swells are named for where they are coming from).

  • “Few are really bad” (Doyle guides).
  • Avoid anchorages open to the North or West!
  • Hurricane swells (season: June to October – ends November 30th) can be from any direction. (Hurricane details from Doyle’s guide).
    • Rarely in December.
    • June; July; October – approximately one every 3 years for:
      • The whole Western Atlantic; including Caribbean Sea and Gulf of Mexico.
    • August; September – approximately 5 per year:
      • Start well out in the Atlantic.
      • Start at the latitude of the Windward Islands.
      • Usually swing north and pass through northern areas of the Caribbean.
      • Very few hit the Windwards sometimes for years at a time.

Christmas Winds (Summary from Doyles Guide)

  • Created by big high pressure systems to the NE.
  • Winds increase (25 – 30kts).
  • Highs can be offset by cold fronts coming down from the Northwest.
    • When approaching: conditions can become calm and sunny followed by wind and rain.
    • These fronts rarely make it as far south as the Windward Islands.

Visibility (From Doyle’s guide)

  • Varies from exceptional lows of 5 miles to a high of over 50 miles.
  • Extremely hazy days caused by dust from Africa.

General Terminology

  • Inter-tropical Convergence Zone –
    • a narrow zone near the equator where northern and southern air masses converge, typically producing low atmospheric pressure. may produce squalls or cloudy weather.
  • Tropical Disturbance, Tropical Wave, and Upper Level Trough –
    • Poorly organized weather systems associated with squalls of varying intensity.
  • Tropical Depression –
    • Organized weather system with sustained winds of up to 35kts and rain.
    • Can be very intense or very weak.
  • Tropical Storm –
    • Sustained winds of 35 to 63kts. (Sustained winds > 64kts = a hurricane).
    • Heavy rains.
  • Tropical Wave –
    • Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which moves from east to west across the tropics causing areas of cloudiness and thunderstorms.
  • Trough –
    • an elongated region of relatively low atmospheric pressure, often associated with fronts. … Unlike fronts, there is not a universal symbol for a trough on a weather The weather charts in some countries or regions mark troughs by a line.
  • Katabatic Winds –
    • from the Greek word κατάβᾰσις katabasis meaning “descending”, is the technical name for a drainage wind, a wind that carries high density air from a higher elevation down a slope under the force of gravity. Such winds are sometimes also called fall winds.

Christmas Winds Detailed Overview.

(http://www.oceannavigator.com/January-February-2012/Christmas-winds/)

 Atlantic Subtropical High:.

  • Located generally between 30° and 35° N.
  • Present in the Atlantic almost all year, but its position shifts with the seasons, and its size and strength also varies.
  • Summer: larger and stronger but located at higher latitudes.
  • During warm to cold season transition:
    • Storm track of lows shifts southward.
    • Creates corresponding shift southward of the subtropical high to approx. 25° to 30° N.
    • High becomes weaker.
    • Induces a stronger pressure gradient between its higher pressure and the lower pressure farther south toward the equator creating stronger SE winds ranging 25-30 knots.
    • Seas can build to 15’ +
  • Areas affected:
    • East of the Bahamas and north of the Antilles (Cuba, Jamaica, Puerto Rico, Hispaniola, Dominican Republic, the Caymans, including the Lesser Antilles: the Leeward and Windward Islands).
    • Northwestern Caribbean (south of Hispaniola and Puerto Rico) can also experience higher than normal seas.
  • As the Storm track becomes more active and shifts further southward:
    • Strong lows move from eastern US into western Atlantic and intensify further south – resulting in:
      • A weakening of the subtropical high
      • The Center of the high shifting further south and east (may even disappear at times).
      • The high moving out of the subtropical latitudes to the eastern Atlantic.
      • Interrupting the flow of the trade winds and,
      • Smaller seas north of the Caribbean islands
      • Possibly creating large swells from the north affecting the north sides of the islands (from strong northerly winds generated by winter storms further north – “north easterlies”
    • Ultimately causing the Christmas winds to abate.

Chris Tibb’s Excellent Overview

I highly recommend to learn more taking a look Chris’ weather site for the Caribbean.

Weather Sources:

Anegada Passage Marine Forecast

Ocean Prediction Center – Atlantic

low bandwidth Graphical Caribbean Offshore Marine Forecasts

Offshore Waters Forecast (Caribbean/SW Atlantic)

NWS Leeward Islands Marine Forecast

Tropical Atlantic GFS (tidbits)

Western Atlantic GFS (tidbits)

Northern Atlantic GFS (tidbits)

NHC Marine Forecasts & Analyses

Meteo France Area Forecast for Antilles-Guyana (Covers Martinique, Guadeloupe, St Bart’s, and St Martin)

Weather Sources While Underway:

Location VHF AM FM Time Details    
BVI”s   780   0805 Mon – Sat    
        0945 Sundays    
        0730 updates hrly on the half 2130
  WX-3            
  WX-4            
  Ch. 16       announced: switch to Ch. 18 and or 85  
USVI: St. Thomas   99.5 0730      
        0830      
        1530      
        1630      
    1000     hrly    
USVI: St. Croix 780          
               
Anguilla     1000   on the hr or the half  
    650   0750 daily    
St. Martin     88.9   on the hr or the half  
      102.7 0900 Sunday nautical program  
  Ch. 10     0730 Cruiser’s net    
  Ch. 12       24hr – recorded  
  Ch. 14     0730 Cruiser’s net (see above)  
  WX-1       24hr – note update frequency  
St. Kitts     92.7   on the hr or the half  
      93.2   on the hr or the half  
Antigua   620   0650      
    650   0750      
    903   0555 Radio Antilles short forecast  
    903   0830 Radio Antilles marine forecast  
      90.5 0750      
      93.9   on the hr or the half  
  Ch. 06     0900 English Harbor Radio m-f local  
Guadeloupe Ch. 16       “hail MRCC in Fort de France – they will  
          give forecast in english” Palvidis  
print
Call Now
Directions