A stormy weather pattern is setting up for this weekend in the Florida Keys. A large and intense spring-time storm system will be evolving over the southern United States and Gulf of Mexico, with periods of rain, thunderstorms, and strong/shifting winds expected in the Florida Keys.
Showers and thunderstorms will increase in coverage and intensity tonight, moving from south to north. Considerable cloudiness is expected Saturday with periods of rain and occasional thunderstorms. Some of the thunderstorms may be "severe" if the proper atmospheric ingredients come together. A "severe" thunderstorm is defined as one with wind gusts of 50 knots or greater and the possibility of large hail. Sustained winds will be out of the south for a good part of the day, with 20-knot sustained winds a possibility (much higher and more variable locally in and near showers and storms).
A surface low pressure area is expected to develop over the eastern Gulf of Mexico by Saturday evening, intensifying as it moves northeastward. The evolution and movement of this low pressure area will have great influence on local wind velocities on Sunday. A considerable degree of uncertainty exists regarding the exact position, intensity, and timing of this low pressure system. As a consequence, the local wind forecast for Sunday is more uncertain than usual. The direction probably will be out of the southwest or west in the morning, shifting to northwest later in the day. Sustained wind speeds could range from near 15 knots to possibly as high as 30 knots, again depending on the position, intensity, and timing of the low. In any case, given the position of the low and the nature of the wind field, a significant westerly swell event looks increasingly likely for Sunday in the southeastern Gulf of Mexico, with westerly swell of at least 7 feet, period 6-7 seconds expected beyond five fathoms. We will try to refine this forecast in each subsequent forecast cycle this weekend.
Attached is a graphic showing the Storm Prediction Center's severe weather outlook for Saturday. All of southern Florida has a "slight risk" of severe thunderstorms. There is a 15% chance of severe weather occurring within 25 miles of any point in the yellow shaded area.
All official National Weather Service watch, warning, and advisory information is available on our web site at:
http://www.weather.gov/keywest