Key West, Florida

New UPDATE, AVIATION

• Coastal flooding will continue to gradually decrease over the weekend, but receding rates will be slow, especially in the Upper Keys.
• Gentle to moderate northeasterly breezes may freshen to moderate to fresh tonight, but are expected to slacken again tomorrow.
• A wet, stormy period is expected tonight through Monday. Locally heavy rainfall, if timed with high tides, may exacerbate coastal flooding hazards.

It has been a difficult evening for trick-or-treat festivities mainly for Key West as a continuous stream of shower and thunderstorm activity has drifted northwestward near and mainly just offshore of the island. While the majority of this activity was just offshore, the lightning activity was very intense at times with many strikes detected within 5 miles of the island during prime trick-or-treating hours, many of which were positive strikes. In addition, these storms were also very efficient rainfall producers with MRMS 3-hr QPE data showing a swath of 3-5" and locally 6" just offshore to the SW of Key West, narrowly avoiding significant flooding impacts on the island. However, even with the majority of the rainfall occurring offshore, an inch to an inch and a half of rainfall occurred from Key West to Boca Chica, which exacerbated the ongoing coastal flooding impacts that have been observed recently. Fortunately, recent KBYX radar imagery finally shows decreasing shower coverage at this time as much of the area is worked over, especially across the Lower Keys. While some additional activity will continue overnight, overall coverage should remain isolated to scattered before increasing in coverage further into Sunday as a shortwave trough brings decreasing heights aloft. Overnight lows will fall to the mid 70s with mostly cloudy to overcast conditions and no changes planned to the ongoing forecast at this time.

A broad high pressure system set up over New England and Pennsylvania. Breezes along the Florida Peninsula freshened last night as the pressure gradient tightened, and the high developed enough to finally push breezes across the Keys back to east-southeasterly. Keys residents could feel the increase in humidity by stepping outside. Dew points across the Keys rose into the upper 70s. Satellite derived Advected Layer PWAT late this afternoon showed an increasing amount of moisture in the 700 to 500 mb layer. This lined up temporally with the development of thunderstorms over the Florida Straits. The environment was in the process of destabilizing and more than sufficient moisture is present. All the environment lacks is a source of lift to organize showers.

An upper level trough, the remnants of Tropical Storm Vance, moved over the northwestern Gulf last night. This shortwave will be able to travel along the Gulf Coast and provide a source of upper level divergence starting early tomorrow morning. The challenge with this trough is that the forcing will not be focused. Ongoing wind convergence south of the Keys is broad. Statistical guidance suggests PoPs may be able to approach 80 percent for portions of the Keys. However, the developing pattern is not one that will last for a long period of time. The region of enhanced divergence will move west of the Keys as early as Monday night. While November may start out with a burst of rainy season weather, we are steadily approaching the dry season.

Once the wet period comes to an end, the forecast for next week becomes more uncertain. While broad layer ridging is expected to prevail across the eastern United States, a strong mid latitude trough is on track to develop over the Great Plains. Exactly how much this trough is able to weaken the ridge is uncertain, and model ensembles are not favoring one solution over another. In essence, the ensembles are moderating the more extreme solutions. Statistical guidance suggests a weak cold front may move across the Keys late next week, but there is no agreement on the timing or magnitude. Check back later, because we will have a better idea of this frontal system after this weekend`s bout of moisture.

Small Craft Should Exercise Caution for increasing winds headlines are in effect for the waters of Florida Bay, Bayside and Gulfside waters, Eastern Hawk Channel, and the eastern Straits of Florida. No additional watches, warnings, or advisories are in effect for the waters surrounding the Florida Keys.

From synopsis: a broad area of high pressure over the eastern United States will sustain gentle to moderate, occasionally fresh, breezes across the FLorida Keys waters this weekend. Small Craft Should Exercise Caution for increasing winds headlines are in effect for portions of the marine zones tonight. Breezes are on track to slacken tomorrow, but stronger winds along the east coast will generate a higher northerly swell for the waters south of the Upper Keys. Expect breezes to slacken during the weekend with light to gentle breezes possible midweek. Shower chances will be elevated through Monday with the peak expected on Sunday. Drier conditions will be able to set up during the middle of the week.

Mainly VFR conditions will prevail through the late evening hours but rain chances will increase Sunday morning into the afternoon hours. As a result, brief MVFR/IFR restrictions will be possible at times if any of this activity brings direct impacts to either of the island chain terminals. Surface winds will be out of the NE at around 5-10 kts, though occasional higher gusts could occur, especially in the vicinity of thunderstorm activity.

On this day in Keys Weather History, in 1999, the daily record rainfall of 4.05" was recorded in Marathon. Precipitation records for Marathon date back to 1950.

FL

Coastal Flood Warning until 5 AM EDT Sunday for FLZ076.

Coastal Flood Advisory until 5 AM EDT Sunday for FLZ077-078.

GM

None.