Marine Weather Net

Florida Bay including Blackwater and Buttonwood Sounds Marine Forecast


TONIGHT

SW
WINDS
10
KNOTS

SATURDAY

VARIABLE
WINDS
5 KNOTS

SATURDAY NIGHT

WSW
WINDS
10
KNOTS

SUNDAY

SW
WINDS
5 - 10
KNOTS

The Marine Weather Forecast In Detail:
GMZ031 Forecast Issued: 420 PM EDT Fri Jul 03 2020

Tonight...South To Southwest Winds Near 10 Knots, Becoming West And Decreasing To Near 5 Knots. Bay Waters A Light Chop, Becoming Smooth. Isolated Showers And Thunderstorms.
Saturday...Variable Winds Near 5 Knots, Becoming Southwest Near 10 Knots In The Afternoon. Bay Waters Smooth, Becoming A Light Chop. Scattered Showers And Thunderstorms.
Saturday Night...Southwest To West Winds Near 10 Knots, Decreasing To Near 5 Knots. Bay Waters A Light Chop, Becoming Smooth. Scattered Showers And Thunderstorms.
Sunday...Southwest Winds 5 To 10 Knots. Bay Waters Smooth To A Light Chop. Scattered Showers And Thunderstorms.
Sunday Night...Variable Winds Near 5 Knots. Bay Waters Smooth. Isolated Showers And Thunderstorms.
Monday...Southeast Winds Near 5 Knots. Bay Waters Smooth. Scattered Showers And Thunderstorms.
Monday Night...East Winds 5 To 10 Knots. Bay Waters Smooth To A Light Chop. Isolated Showers And Thunderstorms.
Tuesday...East To Southeast Winds 5 To 10 Knots. Bay Waters Smooth To A Light Chop. Scattered Showers And Thunderstorms.
Wednesday...East To Southeast Winds 5 To 10 Knots. Bay Waters Smooth To A Light Chop. Scattered Showers And Thunderstorms.
Wednesday Night...East Winds 5 To 10 Knots. Bay Waters Smooth To A Light Chop. Isolated Showers And Thunderstorms.
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Synopsis for Keys coastal waters from Ocean Reef to Dry Tortugas: GMZ005
420 PM EDT Fri Jul 3 2020

An east-west surface ridge axis over the Keys this evening will settle south through the Straits on Saturday, reaching near the north coast of Cuba on Sunday. The ridge will rebound back northward across the Keys on Monday, reaching Central Florida on Tuesday and Wednesday.

Gulf Stream
The Approximate Shoreward Edge of the Gulf Stream as of July 2...
- 20 NM South of Dry Tortugas Light...on Loggerhead Key.
- 24 NM South of Cosgrove Shoal Light...off the Marquesas Keys.
- 28 NM South of Sand Key Light...off Key West.
- 34 NM South of Looe Key...off Big Pine Key.
- 37 NM South of Sombrero Key Light...off Marathon.
- 11 NM Southeast of Alligator Reef Light...off Islamorada.
- 8 NM Southeast of Molasses Reef Light...off Key Largo.
- 8 NM East of Carysfort Reef Light...off Ocean Reef.
Area Forecast Discussion
National Weather Service Key West FL
324pm EDT Fri July 3 2020

The next 7 days will feature near-normal shower and thunderstorm chances, with Sunday's coverage running a bit higher and Monday's coverage running a little lower. Temperatures will average a few degrees above normal.

Day-to-day fluctuations in the weather will mainly vary with movement of an east-west surface ridge axis that is currently shifting slowly southward through the Keys.

Short Term
(Tonight through Monday) Our air mass has moistened over the last 24 hours, with this morning's 12z KEY sounding showing a rise to near-normal PW values. The ridge axis that had kept our PW values (Precipitable Water values) below-normal yesterday has moved south into the Straits. These facts alone will support a rise in shower and thunderstorm activity this weekend.

The ridge axis will continue to sink southward toward the north coast of Cuba by Sunday morning, taking its drying subsidence with it. North of the ridge axis over the Keys, our prevailing flow is already in the process of becoming weak southwesterly. This flow will be favorably parallel to the narrow island chain on Saturday to support cloud line showers and thunderstorms during the day.

A larger-scale enhancement of showers and thunderstorms is expected late Saturday night and Sunday morning. Besides having that ridge axis reach its most southward position, a TUTT low that is currently north of Yucatan Peninsula will meander east toward the Florida Peninsula. The Keys will come under increased upper- level westerly flow and diffluence aloft in the base of the trough. This will serve to deepen our moisture profile and bring a modest increase in larger scale lift. Sunday's forecast will therefore carry the highest rain chances of the 7-day forecast... running in the 35-50 percent range. The higher rain chances will be over the Upper Keys, where westerly flow will try to carry Everglades-borne afternoon thunderstorms eastward across the Upper Keys.

That ridge axis to our south will quickly rebound back north on Sunday night, passing north across the Keys on Monday. A narrow axis of drier air will accompany the ridge, with PW values (Precipitable Water values) progged to quickly but briefly dry out on Sunday night and Monday. Rain chances will drop accordingly.

Long Term
(Tuesday through next Friday) A steady-state extended forecast is in store, with near-normal rain chances in the 20-30 percent range each day. That ridge axis will lift north to near Central Florida on Tuesday and remain there through at least Thursday. Therefore, the Keys will resume typically gentle to occasionally moderate easterly breezes. PW values will average near the 75th percentile for early July (moister than normal), which is a plus for convection. However, 500 mb heigheights will be on the high side in the 591-594 decameter range, supporting increased low-level inhibition as evidenced by marginally hostile forecast 850 mb temps around +19C to +20C. These factors should cancel each other out and ultimately lead to near-normal rain chances with above normal temperatures.

Ensemble means show a weakness in the subtropical ridge developing near our longitude next Friday, which could bring an uptick in activity. Given the strong reliability of climo rain chances in the extended forecast this time of year, will wait before biting off on any increased rain chances.

Marine
An east-west surface ridge axis over the Keys this afternoon will settle south through the Straits on Saturday, reaching near the north coast of Cuba on Sunday. The ridge will rebound back northward across the Keys on Monday, reaching Central Florida on Tuesday and Wednesday.

Close proximity of the ridge axis will hold down wind speeds, with only light to gentle breezes expected through Monday. Once the ridge reaches Central Florida on Tuesday and Wed, then moderate breezes will become possible over the Straits in the evening hours.

Pop-up summertime showers and thunderstorms will be the main concern for mariners.

Climate
On this date in 2019, Marathon recorded a record warm low temperature of 85F.

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