456 FXUS62 KKEY 250904 AFDKEY Area Forecast Discussion National Weather Service Key West FL 504 AM EDT Fri Oct 25 2019 .DISCUSSION... Currently across the Florida Keys, temperatures are in the lower 80s with dew points in the mid 70s. Fresh easterly breezes are occurring across the nearshore and offshore waters, with a Small Craft Advisory now in effect for all of the waters. This has resulted in breezy conditions along the Keys, helping to keep the typical cooler, inland locations from radiating below 80 degrees. Shower coverage has remained mainly widely scattered to isolated overnight, and isolated thunderstorms have struggled to form. The main forecast concern for this package is the immediate short term (next 24 hours) as fresh to strong easterly breezes continue, along with rapidly increasing chances for showers/thunderstorms later this afternoon and into the overnight hours. This is due to an inverted surface trough that is currently producing showers and thunderstorms across far southern portions of the Bahamas and eastern Cuba. This trough axis is progged to lift northwestward into our region over the next 12 hours, accompanied by a long anticipated upper-level low that is moving westward across Cuba along the southern periphery of a deep layer mean ridge centered over the western North Atlantic. These features will result in rapid advection of deep layer moisture beginning this afternoon, with basically no inhibition left to prevent widespread shower formation this evening. In addition, plenty of instability will be present through the profile (modeled surface CAPE approaching 2000 J/kg) to allow for scattered thunderstorms as well. Despite a favorable veering vertical profile, the speed component of the shear vector is almost non-existent with mean flow of 15 to 20 knots from the surface to 500 mb. Therefore not expecting much of a severe threat with any thunderstorms, though strong wind gusts are certainly still possible as convection will already be moving at a fast pace in this flow. That being said, the flow will rapidly decelerate as the trough is lifted northward ultimately into a much larger frontal zone that is pushing eastward across the Gulf. This will slow the translational speed of convection as we head into the overnight hours, which may allow ponding of water in low-lying areas (particularly in areas where storms are able to train). The decelerating flow will result in fresh breezes rapidly slackening to moderate strength as they veer towards the southeast. Unfortunately the aforementioned frontal zone will be unable traverse the entire Gulf and ultimately make it to the Keys. Instead the region will be squeezed into south-southeasterly flow on Saturday and Saturday night, which will allow the Cuban shadow effect to take hold. This should result in a mostly dry Saturday, but chances for convection will still exist, late in the afternoon into the night hours as potential outflow boundaries from Cuba move into the Straits and possibly all the way northward into the Keys. The forward progression of the front will fail on Sunday as retrograding deep layer ridging takes back over. Shower coverage will decrease as a result, with an isolated thunderstorm still possible with enough lingering deep layer moisture (modeled PWATs still near 2.0 inches). Next week will see a return of lower PoPs (20-30%) due to the aforementioned ridge and large scale subsidence. East to southeasterly flow at the surface with a lack of a frontal passage will still allow typical wet season showers to form, though thunderstorms are not expected. Temperatures will remain elevated in the upper 80s for highs and near 80 degrees for lows. && .MARINE... A Small Craft Advisory is in effect for all nearshore and offshore coastal waters of the Florida Keys. Fresh to strong easterly breezes will begin to slacken and veer southeasterly this evening, but rain chances will increase in tandem with widespread showers and scattered thunderstorms developing. Conditions will improve significantly tomorrow, with moderate southeasterly breezes and decreasing chances for showers. Gentle to moderate east to southeasterly breezes will characterize most of the rest of the forecast period. && .AVIATION... VFR and gusty easterly breezes will prevail at the EYW and MTH terminals through the morning. IR satellite imagery reveals a broad cluster of showers and storms moving northwest, between Central Cuba and the southern Bahamas. This region of favored convection is collocated with a surge of tropical moisture. Statistical guidance and satellite derived tracking algorithms place the leading edge of this convection near the terminals around 21Z. Prepare for temporary MVFR CIGS, IFR VIS, and convective wind gusts 25 to 30 knots at either terminal between 21Z and 03Z this evening. && .CLIMATE... On this date in 1903, the daily record cold high temperature of 70 degrees was recorded at Key West. This is also tied for the coldest high temperature ever recorded in October. Temperature records date back to 1872. && .PRELIMINARY POINT TEMPS/POPS... Key West 87 78 87 80 / 50 80 50 60 Marathon 89 78 89 80 / 50 80 50 50 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...Small Craft Advisory for GMZ031>035-042>044-052>055-072>075. && $$ Public/Marine/Fire...WLC Aviation/Nowcasts....CLR Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest