Marine Weather Net

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


TONIGHT

ENE
WINDS
5 - 10
KNOTS

FRIDAY

E
WINDS
10 - 15
KNOTS

FRIDAY NIGHT

E
WINDS
10
KNOTS

SATURDAY

E
WINDS
10 - 15
KNOTS

The Marine Weather Forecast In Detail:
GMZ054 Forecast Issued: 445 PM EDT Thu Apr 02 2020

Tonight...Northeast To East Winds 5 To 10 Knots. Seas 2 To 4 Feet, Except 5 Feet In North Swell Off The Upper Keys.
Friday...East Winds 10 To 15 Knots. Seas 2 To 4 Feet.
Friday Night...East Winds Near 10 Knots, Increasing To 10 To 15 Knots. Seas 2 To 4 Feet.
Saturday...East Winds 10 To 15 Knots. Seas 2 To 3 Feet.
Saturday Night...East To Southeast Winds 10 To 15 Knots. Seas 2 To 4 Feet.
Sunday...East To Southeast Winds 10 To 15 Knots. Seas 2 To 4 Feet. Isolated Showers.
Sunday Night...East To Southeast Winds 10 To 15 Knots. Seas 2 To 5 Feet. Isolated Showers.
Monday And Monday Night...East To Southeast Winds 15 To 20 Knots. Seas 3 To 6 Feet. Isolated Showers.
Tuesday...East To Southeast Winds 10 To 15 Knots. Seas 3 To 5 Feet. Isolated Showers.
Tuesday Night...Southeast Winds 10 To 15 Knots. Seas 2 To 4 Feet.
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Synopsis for Keys coastal waters from Ocean Reef to Dry Tortugas: GMZ005
445 PM EDT Thu Apr 2 2020

A high pressure ridge from the Great Lakes to North Florida will slowly move east, emerging over the Atlantic late Saturday. A better defined high pressure cell will then form northeast of the Bahamas on Sunday, extending a ridge westward across North Florida on Monday. That ridge axis will settle south down the Florida Peninsula on Tuesday, bringing a decrease to gentle and moderate easterly breezes.

Gulf Stream
The Approximate Shoreward Edge of the Gulf Stream as of April 2...
- 34 NM South of Dry Tortugas Light...on Loggerhead Key.
- 20 NM South of Cosgrove Shoal Light...off the Marquesas Keys.
- 20 NM South of Sand Key Light...off Key West.
- 23 NM South of Looe Key...off Big Pine Key.
- 23 NM South of Sombrero Key Light...off Marathon.
- 15 NM Southeast of Alligator Reef Light...off Islamorada.
- 11 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
309pm EDT Thu April 2 2020

Weather over the next 7 days will be uneventful for the Florida Keys. Easterly breezes will freshen from Sunday through Monday night, then ease in the middle of the week. Temperatures will rise well above normal toward the middle of next week. Otherwise, dry weather will prevail with rain chances topping out at only about 10-15 percent on Monday.

Short Term
(Tonight through Saturday night) The air mass was very dry on the 12z KEY sounding this morning, with Precipitable Water (PW) value of 0.63", or below the 10th percentile for this week of the year. Winds have turned easterly today, and dewpoints have responded by rising back into the mid 60s. Late this evening and overnight, several pieces of CAMS guidance develop a few weak showers near the Keys, with the HRRR (High-Resolution Rapid Refresh) focusing along a surface boundary that is readily apparent in visible satellite imagery stretching southeast from the Lower Keys. CIMMS MIMIC PW imagery shows a tongue of PW values (Precipitable Water values) in excess of 1" near this slow-moving boundary. Have therefore added dime PoPs as acknowledgement of the possibility of a few weak showers later tonight.

Otherwise, PW values (Precipitable Water values) on Friday and Saturday will steady off around 1.1". At most, the Gulf waters could get the leftovers each evening of an afternoon shower moving westward off Mainland Monroe County. The rest of the forecast domain will be confidently shower-free. Winds will be light to gentle considering a high pressure ridge pointed from the Great Lakes down into Florida. Temperatures will be near normal, and dewpoints will hold at comfortable levels in the 60s. Overall, pretty delightful weather.

Long Term
(Sunday through next Thursday) An upper ridge will begin to amplify from the Yucatan into the central Gulf on Sunday, peaking in strength from the Yucatan Channel into the eastern Gulf on Tuesday. It will start to weaken and flatten next Wednesday night and Thu.

For Sunday and Monday, this will put Florida in northwest flow aloft downstream of the ridge axis. For days, models have been pointing to an upper impulse rounding the ridge and supporting MCS development over the north-central Gulf on Sunday. The MCS would then move east-southeast through the eastern Gulf, dying off late Sunday night or Monday morning before reaching the Keys. Nonetheless, the upper impulse or ghost MCV could spark a few showers. Monday might be a day to watch for development over the Everglades that could then move east-southeast across the far Upper Keys. Even aside from this possibility, low-level easterly flow will freshen on Sunday night and Monday as well, bringing a healthy rise in PW values (Precipitable Water values) and infusing the possibility for mesoscale speed surges to provide small-scale focus for shallower shower activity. Have therefore continued with the 10-15 percent rain chances in the forecast areawide for Sunday, Sunday night and Monday, with a lingering dime Probability of Precipitation on Tuesday.

That upper ridge will exert maximum influence over the Keys next Tuesday night and Wed, concurrent with an easing of low-level winds as an east-west surface ridge axis settle south across the forecast area. This pattern supports the shower-free forecast for Tuesday night through Wednesday night.

The ridge will start to flatten and weaken next Thursday (Day 7). The surface ridge axis will have moved south of the Keys by then, with southwest or westerly low-level flow developing. Surface dewpoints climb back into the lower 70s around the middle of next week, and surface-based instability starts to creep up. GEFS plumes for HST show a nice bump in Quantitative Precipitation Forecast-producing ensemble members next Thursday, though not for EYW. This might suggest afternoon convection over the southern peninsula that then gets steered out across the far Upper Keys in west flow aloft. Have gone with dime PoPs in the grids over the Upper Keys for this possibility.

All of this seems a bit hair-splitty, but that is the nature of forecasting in an otherwise uneventful week.

Marine
No advisories or headlines are in effect, and none appear possible until about Sunday night or Monday.

From synopsis...A high pressure ridge from the Great Lakes to North Florida will slowly move east, emerging over the Atlantic late Saturday. A better defined high pressure cell will then form northeast of the Bahamas on Sunday, extending a ridge westward across North Florida on Monday. That ridge axis will settle south down the Florida Peninsula on Tuesday, bringing a decrease to gentle and moderate easterly breezes.

Climate
In 1987, after a high of 65F and low of 56F the previous day (the 1st), the low temperature of 48F at Key West International Airport on the 2nd shattered the cold record for the date. It is the lowest temperature ever recorded in Key West in the month of April (with the next-lowest being 54F in 1891), and the next- latest sub-50F reading ever is 49F on March 04, 1980.

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