Marine Weather Net

Straits of Florida from Halfmoon Shoal to 20 NM west of Dry Tortugas out 20 NM Marine Forecast


THIS AFTERNOON

SE
WINDS
15 - 20
KNOTS

TONIGHT

E
WINDS
20
KNOTS

MONDAY

SE
WINDS
20
KNOTS

MONDAY NIGHT

SE
WINDS
20 - 25
KNOTS

The Marine Weather Forecast In Detail:
GMZ055 Forecast Issued: 958 AM EDT Sun Oct 25 2020

SMALL CRAFT SHOULD EXERCISE CAUTION UNTIL WINDS DECREASE ...SMALL CRAFT MAY BE REQUIRED TONIGHT...
This Afternoon...Southeast Winds 15 To 20 Knots, Decreasing To Near 15 Knots. Seas 4 To 5 Feet. Scattered Showers And Thunderstorms In The Morning, Then Numerous Showers And Isolated Thunderstorms In The Afternoon.
Tonight...East To Southeast Winds Increasing To Near 20 Knots. Seas 4 To 6 Feet. Numerous Showers And Isolated Thunderstorms.
Monday...Southeast Winds Near 20 Knots. Seas 6 To 7 Feet. Scattered Showers And Isolated Thunderstorms.
Monday Night...Southeast Winds 20 To 25 Knots, Decreasing To 15 To 20 Knots Late. Seas 5 To 7 Feet. Scattered Showers And Isolated Thunderstorms.
Tuesday...East To Southeast Winds 15 To 20 Knots. Seas 3 To 5 Feet. Scattered Showers And Isolated Thunderstorms.
Tuesday Night...East To Southeast Winds Near 15 Knots. Seas 3 To 4 Feet. Scattered Showers And Isolated Thunderstorms.
Wednesday And Wednesday Night...East To Southeast Winds Near 15 Knots. Seas 3 To 4 Feet. Isolated Showers And Thunderstorms.
Thursday...East To Southeast Winds 10 To 15 Knots. Seas 2 To 4 Feet. Isolated Showers And Thunderstorms.
Thursday Night...East To Southeast Winds Near 10 Knots. Seas 2 To 3 Feet. Isolated Showers And Thunderstorms.
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Synopsis for Keys coastal waters from Ocean Reef to Dry Tortugas: GMZ005
958 AM EDT Sun Oct 25 2020

Tropical Storm Zeta will move slowly northwestward, passing through the Yucatan Channel on Monday. Then an Atlantic ridge axis will build westward across the Florida Peninsula from Tuesday through Thursday, bringing an easing of southeast breezes.

Gulf Stream
The Approximate Shoreward Edge of the Gulf Stream as of October 24...
- 25 NM South of Dry Tortugas Light...on Loggerhead Key.
- 35 NM South of Cosgrove Shoal Light...off the Marquesas Keys.
- 41 NM South of Sand Key Light...off Key West.
- 41 NM South of Looe Key...off Big Pine Key.
- 39 NM South of Sombrero Key Light...off Marathon.
- 20 NM Southeast of Alligator Reef Light...off Islamorada.
- 14 NM Southeast of Molasses Reef Light...off Key Largo.
- 10 NM East of Carysfort Reef Light...off Ocean Reef.
Area Forecast Discussion
National Weather Service Key West FL
1058am EDT Sunday Oct 25 2020

Currently - It was a rather quiet and uneventful morning until about an hour ago. Taking a look at radar trends precipitation was struggling this morning to develop. What precipitation did form actually moved in opposing direction. Showers and isolated thunderstorms over the far eastern waters were and still are moving to the northeast. Meanwhile, showers over the far western waters were and still are moving to the north-northwest. This is all in spite of a surface wind from the southeast. This suggests that we have a divergent flow just above the boundary layer which is making for a precipitation hole across a majority of our CWA this morning.

With that being said, shower coverage is on the increase, mostly in the western waters where a speed convergence is occurring. We have winds of 10 to 15 knots over these waters encountering lesser speeds over the extreme southeast Gulf just along our AOR. Otherwise, it's been mostly cloudy despite the lack of precipitation, thanks to widespread isentropic upglide. Taking a look at visible satellite, we have an almost fairly uniform flat altocumulus deck across the eastern two-thirds of our CWA. This is indicative that we have gentle upglide occurring. As a result of the extensive cloud deck, temperatures are holding in the lower 80s.

Short Term Update
Given the challenges this morning with the forecast, have made quite a bit of changes to the first period forecast. First made changes to probability of precipitation in the first period. Given the seemingly divergent flow just off the surface, have lowered probability of precipitation for this morning. For now have made the Middle and Upper Keys chance probability of precipitation (30-40 percent) and the Lower Keys slight chance (20 percent). Moisture is more than adequate as evident by this morning's 12Z ROB sounding which measured a PWAT (Precipitable Water) of 2.37 inches, which breaks the daily record of 2.30 inches. Once the flow becomes more convergent, precipitation will become likely, which looks to occur this afternoon or early evening.

The second change was made to the coastal waters forecast. Winds have not come up and actually have come down from previous thinking. As such will keep winds highest over the Florida Straits but will decrease everywhere else. Winds are forecast to decrease slightly further for the afternoon before rising tonight.

Otherwise, made no other changes beyond the first period. Tropical Storm Zeta has not made much way in either movement or intensity. Zeta remains located about 275 miles southeast of Cozumel with a present movement of 0 mph. Zeta will slowly meander northwest over the next couple of days and eventually emerge over the southern Gulf of Mexico. In the meantime, tropical moisture associated with Zeta will transport northward over the next 24 to 36 hours, leading to higher rain chances and the potential for heavy rain and localized flooding, especially when combined around times of high tide.

Marine
Gentle to moderate southeast breezes prevail for the majority of our waters with the exception of the Florida Straits, where a brief period of moderate to fresh breezes will persist this morning. However, winds are expected to slacken for the afternoon for these waters. As such a Small Craft Exercise Caution (SCEC) headline is effect for the Florida Straits only. Breezes will freshen tonight with additional SCEC headlines likely. In addition, there is a potential that winds may freshen such that Small Craft Advisories may be needed for all or at least portions of the marine district.

Meanwhile, Zeta will slowly trek north and northwest over the next several days. Its presence relatively close by will keep the gradient such that moderate to fresh with potentially strong breezes, will be possible on Monday and Monday night. Thereafter it will move far enough away that ridging will return and breezes will quickly slacken Tuesday through the end of the week.

NOAA Key West FL Office: Watches - Warnings - Advisories
FL...None. GM...None.