Marine Weather Net

Florida Bay including Blackwater and Buttonwood Sounds Marine Forecast


TODAY

SSE
WINDS
5 KNOTS

TONIGHT

SSE
WINDS
5 KNOTS

TUESDAY

S
WINDS
10
KNOTS

TUESDAY NIGHT

SSW
WINDS
5 KNOTS

The Marine Weather Forecast In Detail:
GMZ031 Forecast Issued: 412 AM EDT Mon Sep 28 2020

Today...Southeast To South Winds Near 5 Knots. Bay Waters Smooth. Scattered Showers And Thunderstorms.
Tonight...Southeast To South Winds Near 5 Knots, Increasing To Near 10 Knots After Midnight. Bay Waters Smooth, Becoming A Light Chop. Scattered Showers And Isolated Thunderstorms.
Tuesday...Southeast To South Winds Near 10 Knots. Bay Waters A Light Chop. Scattered Showers And Isolated Thunderstorms In The Morning, Then Isolated Showers In The Afternoon.
Tuesday Night...South To Southwest Winds Near 5 Knots. Bay Waters Smooth. Scattered Showers And Isolated Thunderstorms.
Wednesday...Southwest To West Winds Near 5 Knots, Becoming Northwest To North 5 To 10 Knots Late In The Afternoon. Bay Waters Smooth, Becoming Smooth To A Light Chop. Scattered Showers And Isolated Thunderstorms.
Wednesday Night...North To Northeast Winds 10 To 15 Knots. Bay Waters A Light To Moderate Chop. Scattered Showers And Isolated Thunderstorms.
Thursday...Northeast Winds Near 10 Knots. Bay Waters A Light Chop. Scattered Showers And Isolated Thunderstorms.
Thursday Night...Northeast Winds 10 To 15 Knots. Bay Waters A Light To Moderate Chop. Numerous Showers And Isolated Thunderstorms.
Friday...Northeast Winds 10 To 15 Knots. Bay Waters A Light To Moderate Chop. Numerous Showers And Isolated Thunderstorms.
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Synopsis for Keys coastal waters from Ocean Reef to Dry Tortugas: GMZ005
412 AM EDT Mon Sep 28 2020

Light to gentle, mostly southeast breezes will prevail today through Tuesday morning, becoming southerly Tuesday afternoon and Tuesday night as a cold front approaches from the Gulf of Mexico. This front will slide southeast through the Keys waters Wednesday afternoon and evening, with freshening north to northeast breezes. Moderate to occasionally fresh northeast breezes are expected Thursday through Friday night.

Gulf Stream
The Approximate Shoreward Edge of the Gulf Stream as of September 26...
- 51 NM South of Dry Tortugas Light...on Loggerhead Key.
- 33 NM South of Cosgrove Shoal Light...off the Marquesas Keys.
- 26 NM South of Sand Key Light...off Key West.
- 19 NM South of Looe Key...off Big Pine Key.
- 18 NM South of Sombrero Key Light...off Marathon.
- 11 NM Southeast of Alligator Reef Light...off Islamorada.
- 6 NM Southeast of Molasses Reef Light...off Key Largo.
- 6 NM East of Carysfort Reef Light...off Ocean Reef.
Area Forecast Discussion
National Weather Service Key West FL
422am EDT Monday September 28 2020

Radar detects scattered showers across the area, with the activity showing very little movement, and only an occasional lightning strike detected. Skies are partly cloudy over the Keys, as high cloudiness streams southward from active deep convection over central Florida. Temperatures along the island chain are hovering in the lower 80s, and winds are mostly from the SE at 5 mph or less. Surface analysis shows a weak surface ridge extending from the western Atlantic across extreme south Florida and into the far southeastern Gulf of Mexico. Aloft, weak but deep layered ridging continues to prevail across the Keys and South Florida. The 00Z Key West sounding measured a moist and conditionally unstable profile, with a PW value of 2.22 inches (above the 90th percentile for this date) and no significant inversions noted. MIMIC-TPW satellite imagery shows a similarly moist airmass surrounding the Keys, with a considerably drier airmass (estimated PW values (Precipitable Water values) of 1.5 to 1.7 inches) extending from south of Andros Island to north of Hispaniola.

For today, very weak flow along with abundant moisture and no suppressing inversions or dry layers aloft should allow mesoscale convective processes to flourish, with a possible island cloud line, existing meandering boundaries, and outflows from afternoon convective development over the adjacent larger land masses all acting as possible triggers. Have continued with slightly above climo 40 percent PoPs. Rain chances should ease downward starting late tonight and especially by Tuesday afternoon, as the drier airmass mentioned above edges westward into at least part of the Keys, and more defined SSW low level flow brings the typical daytime Cuban convective shadow overhead. This same flow may then allow Cuban convection/outflows to move NNE toward the Keys Tuesday evening, but it may struggle to sustain itself, depending on how much of the dry airmass infiltrates into our area from the east.

Guidance remains consistent with the evolution of an unseasonably deep trough aloft over the eastern CONUS through this week, which will drive an early season cold front across the Gulf of Mexico, with the front still forecast to reach our offshore Gulf waters late Wednesday morning, then move through the Keys during the afternoon and evening hours. The front then stalls somewhere over the eastern Straits for the remainder of the week and into next weekend. Guidance shows a well-defined mid-level cyclonic gyre developing over Central America and the western Caribbean during the later part of the week, with copious moisture streaming northward within the NE quadrant of this circulation and overrunning the stalled frontal boundary near the Keys. We continue to expect a prolonged period of unsettled and wet weather for the later part of the week and into the weekend, with periods of heavy rainfall possible, and have nudged Probability of Precipitation up to 60 percent for Thursday night through Saturday night. Temperatures should fall back to near normal for this time of year (lows in the upper 70s and highs in the mid-upper 80s) due to the increased cloud cover and rainfall.

Marine
Overnight observations show light breezes over the Keys coastal waters, becoming SE during the past couple of hours. Generally benign wind and sea conditions will continue across the area today through Tuesday night, with isolated to scattered thunderstorms, and perhaps a few waterspouts once again today along cloud lines over the nearshore waters being the only real weather concerns. An early season cold front will move across the Gulf of Mexico from late today through Tuesday night, and is then forecast to move across the Keys waters Wednesday afternoon and evening, before stalling over the eastern Florida Straits on Thursday. We are forecasting moderate NE breezes behind this front for the later part of the week, although they could be stronger or weaker at times depending on exactly where the front stalls out. A northwest swell is also forecast to push into our waters Wednesday, causing building seas across the Gulf waters and western Straits. This swell should peak Wednesday evening and then subside on Thursday.

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