Marine Weather Net

Straits of Florida from west end of Seven Mile Bridge to south of Halfmoon Shoal out 20 NM Marine Forecast






5 - 10


5 - 10

The Marine Weather Forecast In Detail:
GMZ054 Forecast Issued: 421 AM EST Sat Jan 16 2021

Today...Northwest Winds Near 20 Knots, Decreasing To 15 To 20 Knots In The Afternoon. Seas 3 To 6 Feet. Isolated Showers In The Morning.
Tonight...Northwest Winds Near 15 Knots, Becoming Northwest To North And Decreasing To 10 To 15 Knots. Seas 3 To 6 Feet, Highest West Of Cosgrove Shoal Light Due To Northwest Swell.
Sunday...North To Northeast Winds 5 To 10 Knots. Seas 3 To 6 Feet, Highest West Of Cosgrove Shoal Light Due To Northwest Swell.
Sunday Night...Northwest To North Winds 5 To 10 Knots. Seas 2 To 4 Feet Due To Northwest Swell. Isolated Showers.
Monday...North Winds Near 10 Knots, Becoming North To Northeast And Increasing To 10 To 15 Knots In The Afternoon. Seas 1 To 3 Feet.
Monday Night...Northeast Winds Increasing To 15 To 20 Knots. Seas Building To 3 To 5 Feet.
Tuesday...Northeast To East Winds 15 To 20 Knots. Seas 4 To 6 Feet.
Wednesday...Northeast To East Winds 15 To 20 Knots. Seas 4 To 6 Feet.
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Synopsis for Keys coastal waters from Ocean Reef to Dry Tortugas: GMZ005
421 AM EST Sat Jan 16 2021

A cold front will exit the Florida Straits early this morning. Fresh northwest breezes will prevail behind the front today, then become north and quickly diminish tonight. High pressure will move slowly east along the northern Gulf Coast Sunday through Monday, with gentle north to northeast breezes prevailing across the Keys. This high will strengthen over the Southeastern United States Monday night and Tuesday, with fresh northeast to east breezes over the Keys waters. The high will then settle slowly southward across the Florida peninsula on Wednesday, allowing breezes to relax somewhat.

Gulf Stream
The Approximate Shoreward Edge of the Gulf Stream as of January 16...
- 54 NM South of Dry Tortugas Light...on Loggerhead Key.
- 34 NM South of Cosgrove Shoal the Marquesas Keys.
- 29 NM South of Sand Key Key West.
- 25 NM South of Looe Big Pine Key.
- 23 NM South of Sombrero Key Marathon.
- 18 NM Southeast of Alligator Reef Islamorada.
- 16 NM Southeast of Molasses Reef Key Largo.
- 9 NM East of Carysfort Reef Ocean Reef.
Area Forecast Discussion
National Weather Service Key West FL
420am EST Sat Jan 16 2021

The cold front moved through the Keys island chain overnight as expected, preceded by brief heavy downpours at some locations. Currently radar shows the shower band ahead of the front exiting the eastern Straits. Skies remain mostly cloudy along the Keys, with temperatures in the upper 60s, and winds on land are from the northwest around 15 mph. Satellite imagery depicts a massive gyre spinning over the Midwest and anchoring a large trough which dominates the entire eastern half of the CONUS. An active subtropical jet streaking to the south of this trough continues to bring high cloudiness over the Keys and South Florida. The 00Z Key West sounding sampled a moist pre-frontal airmass, but recent MIMIC-TPW imagery shows a much drier airmass, with estimated PW values well below an inch, moving quickly SE across the eastern Gulf of Mexico and toward the Keys.

For today, expect partly cloudy, dry and slightly cooler conditions, as northwest winds gradually diminish during the day. High temps will only be a couple of degrees cooler than were observed on Friday, likely reaching around 70 degrees. Quickly decreasing north breezes tonight may allow for some radiational cooling, although we will continue to see more cloud cover than we typically do post-frontal, as mid/high level moisture will continue to stream overhead. Sunday will be another cool and dry day, with highs probably failing to reach 70 degrees.

Heading into Sunday night, the next shortwave passing by well to our north will induce increasing mid/upper level moisture and lift within the subtropical jet, but model cross-sections show dryness persisting in the 850-700 mb layer. Have maintained 20 percent PoPs, although model guidance Probability of Precipitation continue to vary greatly due to differences in the predicted northward extent of the moisture return. Thereafter, dry weather and a slow warming trend will prevail through next week as flat ridging gradually builds northward from the Caribbean. Temps will remain slightly below normal through Tuesday, return to near normal on Wednesday, and creep slightly above normal for Thursday and Friday.

Northwest winds have been somewhat anemic behind the advancing cold front thus far, with Smith Shoal Light and Sand Key only running in the 15-17 knot range during the past couple of hours. There is still the potential for winds to be enhanced over the warmer waters of the offshore Straits, and will keep the Small Craft Advisory posted there today. SCA (Small Craft Advisory) will also remain posted for the offshore Gulf waters, due to seas building up to 7 feet during the day. Elsewhere, Small Craft Exercise Caution headlines will be posted for NW winds of 15 to 20 knots. These winds are expected to decrease quickly this evening, with the only remaining marine hazards for tonight being 7 foot seas over the offshore Gulf waters and Lower Straits due to lingering NW swell. Light to gentle mostly northerly breezes are expected for Sunday into Monday, followed by increasing NE winds from late Monday into Tuesday. SCEC headlines will likely return during this time, with SCA (Small Craft Advisory) possible.

NOAA Key West FL Office: Watches - Warnings - Advisories
FL...None. GM...Small Craft Advisory for GMZ033-034-052>055-072>075.