Straits of Florida from Halfmoon Shoal to 20 NM west of Dry Tortugas out 20 NM Marine Forecast
|Tonight...Northeast To East Winds Near 20 Knots, Decreasing To 15 To 20 Knots. Seas 5 To 7 Feet, Subsiding To 4 To 6 Feet.|
|Wednesday And Wednesday Night...Northeast Winds 15 To 20 Knots. Seas 4 To 6 Feet.|
|Thursday...Northeast Winds Near 15 Knots, Becoming East And Decreasing To 10 To 15 Knots. Seas 3 To 5 Feet.|
|Thursday Night...East Winds 10 To 15 Knots, Becoming East To Southeast And Decreasing To Near 10 Knots. Seas 2 To 4 Feet.|
|Friday...Southeast Winds Near 10 Knots, Becoming South To Southwest And Decreasing To 5 To 10 Knots. Seas 2 To 3 Feet, Subsiding To 1 To 2 Feet.|
|Friday Night...Variable Winds Near 5 Knots, Becoming Northeast To East After Midnight. Seas 1 To 2 Feet.|
|Saturday...Northeast Winds 5 To 10 Knots. Seas 1 To 2 Feet.|
|Saturday Night...Northeast To East Winds 10 To 15 Knots. Seas 2 To 3 Feet.|
|Sunday...East Winds 10 To 15 Knots. Seas 2 To 4 Feet. Isolated Showers.|
|Sunday Night...East Winds Near 15 Knots, Increasing To 15 To 20 Knots. Seas 3 To 5 Feet, Building To 4 To 6 Feet.|
| Synopsis for Keys coastal waters from Ocean Reef to Dry Tortugas: GMZ005|
424 PM EST Tue Jan 19 2021
A strong high pressure center over far northern Florida will elongate into an east-west ridge tonight. The ridge will settle slowly south down the Florida Peninsula on Wednesday and Thursday. The ridge will reach South Florida on Friday before dissipating on Saturday. A new high center will drop southeast off the Carolina coast on Sunday, bringing a freshening northeast breeze on Sunday which will then turn easterly on Sunday night.
The Approximate Shoreward Edge of the Gulf Stream as of January 19...
- 15 NM South of Dry Tortugas Light...on Loggerhead Key.
- 6 NM South of Cosgrove Shoal Light...off the Marquesas Keys.
- 5 NM South of Sand Key Light...off Key West.
- 6 NM South of Looe Key...off Big Pine Key.
- 7 NM South of Sombrero Key Light...off Marathon.
- 4 NM Southeast of Alligator Reef Light...off Islamorada.
- 2 NM Southeast of Molasses Reef Light...off Key Largo.
- 5 NM East of Carysfort Reef Light...off Ocean Reef.
| Area Forecast Discussion|
National Weather Service Key West FL
314pm EST Tuesday Jan 19 2021
A cool and dry air mass continues to prevail over the Keys this afternoon, with high temperatures topping out in the lower to mid 70s. This is a degree or two below normal for mid-January. Dewpoints are in the comfortable upper 50s to near 60F. The 12z KEY sounding showed a strong subsidence inversion based near 5,500 feet, but the dry air mass is only supporting a few fair weather cumulus moving in from Hawk Channel. A dry PW value of 0.80" precludes any shower activity. A fresh NE-E breeze continues.
Much of this winter has been characterized by cold frontal passages 1-3 times a week, leading to below-normal temperatures on average since the start of December. However, a large-scale change in the pattern will disrupt this rhythm for the next 7-10 days.
The strong upper high just north of Puerto Rico this afternoon will retrograde west, arriving near the Yucatan Peninsula late Wednesday and Thursday. It will then extend a flat ridge north through the eastern U.S. this weekend, as upper troughing shifts out toward the western U.S.. This is an unfavorable pattern for pushing cold fronts this far south. Meanwhile, nearby proximity of upper level high pressure will come with warm and dry mid- level air, which caps surface-based lift before showers even have a chance to develop. The official forecast therefore carries near- zero rain chances through Sunday. In the absence of any cold fronts and with surface winds turning more east-southeasterly on Thu and Fri, a warming trend will get underway on Thursday and accelerate on Friday.
A back door cold front will try to spread in from the northeast around Sunday or Sunday night. However, it will wash out as it spreads southeast down the Keys and only warrants a 10-percent rain chance. Its main impact will be a freshening northeast breeze on Sunday night, which will then quickly clock southeasterly by Monday. It will barely even interrupt the prolonged warming trend.
Ensemble means show the nearby upper high strengthening even more toward the middle of next week. A return to near-zero rain chances is forecast, and next Tuesday should feature the majority of island locations finally reaching 80 or higher.
A Small Craft Advisory is in effect for the western Straits, west of a line extending south from the Seven Mile Bridge. This is where winds will flirt with 20+ knots at times through this evening, and where seas will therefore have the best shot of reaching 7 feet. Elsewhere, fresh NE-E breezes mean that Small Craft Should Exercise Caution.
On this date in 1997, the daily record low temperature of 45F and 48F was last recorded at Marathon and Key West respectively.
NOAA Key West FL Office: Watches - Warnings - Advisories
FL...None. GM...Small Craft Advisory for GMZ054-055-074-075.