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Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
726 FXUS62 KKEY 070829 AFDKEY Area Forecast Discussion National Weather Service Key West FL 429 AM EDT Sun Jul 7 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 429 AM EDT Sun Jul 7 2024 Relict island cloud lines activated around midnight along parts of the Upper Keys and just north of the Lower Keys, but that activity was pushed WNW into the Bay and Gulf waters by developing weak ESE low level flow, and radars currently detect only isolated showers dotting the region. Temperatures along the island chain are hovering in the mid 80s, with dewpoints in the mid to upper 70s, and winds on land generally from the east to southeast at 5 to 10 mph. Surface analysis depicts a weak pressure gradient across our area, between high pressure over the western Atlantic, a tropical wave over the western Caribbean Sea, and Tropical Storm Beryl over the western Gulf of Mexico. Aloft, mid level ridging prevails over Florida, between Beryl to the west and a well-defined Tropical Upper Tropospheric Trough (TUTT) cell northeast of the Bahamas. The 00Z Key West sounding measured PW of 2.20 inches (over the 90th percentile for the date). More recent GOES-TPW satellite imagery shows a slightly drier airmass, with estimated PWs between 1.8 and 1.9 inches, moving across the Florida Straits toward the Keys. For today, there are conflicting signals as to rain chances, with the slightly drier airmass expected for at least this morning, along with the current weak ESE low level flow, appearing not especially favorable for rainfall. The CAM guidance is also rather dry through much of the day. On the other hand, we do expect a surge of moisture along with increasing SSE flow later in the day as the tropical wave over the western Caribbean passes to our south, and the MOS/NBM guidance has fairly high rain chances. Have opted to maintain the existing 40 percent PoPs for today. The best rain chances may occur from later in the afternoon through the evening hours when the deepest moisture along the northern edge of the tropical wave passes through our area. Otherwise, expect typical summertime temps and dewpoints for today, with highs near 90 at most locations. Monday through Tuesday, a much drier airmass associated with a Saharan Air Layer (SAL) moves across the Keys, with PWs plummeting to below 1.5 inches. Rain chances will be minimal during this time, with the main concern being heat as high temps climb into the lower 90s. Heat advisories may be needed both days. By Wednesday, the TUTT cell currently located northeast of the Bahamas is forecast to be centered nearby, although not as well-defined as it is currently. With ample moisture returning to our area behind the departing SAL, have maintained above climo 40 percent PoPs. Thereafter, we should remain in a typical midsummer pattern, with gentle easterly flow pattern to the south of the Atlantic ridge. Daily rain chances will be modulated by subtle changes in moisture, stability and steering flow, along with any passing weak tropical waves. For now, have maintained 30 percent PoPs, which is slightly above climo, but slightly below the MOS consensus. Temps will remain near normal, with highs around 90, and lows in the lower to mid 80s outside of any brief downpours. && .MARINE... Issued at 429 AM EDT Sun Jul 7 2024 After remaining light and variable through much of the night, 4 AM obs show the expected SE breezes of of 5 to 10 knots kicking in along the reef and at Long Key C-MAN. No marine headlines are currently in effect, and none are expected through the next several days. From the synopsis, gentle southeast to south breezes will continue across the Keys coastal waters through Monday, between high pressure over the western Atlantic and Tropical Storm Beryl over the western Gulf of Mexico. High pressure will build westward across the Florida peninsula and into the Gulf beginning Tuesday, bringing gentle to occasionally moderate easterly breezes to the Keys waters. && .AVIATION... (06Z TAFS) Issued at 429 AM EDT Sun Jul 7 2024 VFR conditions will prevail through the TAF period at both EYW and MTH with southeasterly near-surface winds of 5 to 10 knots. There is a possibility of scattered showers and isolated thunderstorms later today, but confidence is low with respect to timing, so opting to keep VCSH out of the TAFs for now. && .CLIMATE... On this day in 2023, both the daily record warm low temperature of 84F and the daily record high temperature of 96F were recorded in Marathon. Temperature records for Marathon date back to 1950. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && $$ Public/Marine/Fire...Jacobson Aviation/Nowcasts....DP Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest