National Weather Service Tampa Bay Ruskin FL
748pm EDT Wednesday August 21 2024
Issued at 300pm EDT Wednesday August 21 2024
An amplified pattern is in place with an upper-level low over New England and a trough axis stretched across the E CONUS. A stationary front is parked over Central Florida in response, with the I-4 corridor remaining the delineation line from a drier and more stable airmass to a warm and humid deep summer airmass. Nature Coast counties have seen no storms today, even as the West Coast sea breeze moves inland. Meanwhile, SWFL remains saturated and unstable, with several rounds of showers and thunderstorms developing today.
This boundary has kept a WSW flow in place, and continues to serve as a focal point for convective initiation. Additional storms are expected to continue developing through the afternoon and into the evening, before a period of reprieve is likely overnight, given the loss of diurnal heating. However, the southwest flow favors an early start again tomorrow. By 5 to 6AM, coastal showers and thunderstorms are likely across the West Coast of the Florida peninsula; and unlike today, should be farther north and not just over central and SWFL.
The frontal boundary is expected to lift north slightly overnight as the parent trough does the same. This favors the moisture axis setting up slightly farther north tomorrow, yielding more consistent opportunities for storms across the region. This will slowly continue to modify over the next couple days thereafter, with a WSW flow and morning storms favored until the flow changes later this week.
While a weak upper-level low could form by late week over N FL and S GA, this won't change the outcome much, and ultimately should usher in the return of a more ESE flow as the week turns to the weekend. With that flow change, widespread, deep tropical moisture - more so than we are seeing currently - returns as well. PWATs (Precipitable Waters) are consistently coming in around 2 inches areawide, which favors scattered to numerous afternoon and evening thunderstorms each day through next week.
The main concern through the next week will be heavy rainfall, gusty winds, and frequent lightning. A relatively warm, humid, and mostly static atmosphere across the region will not support any organized severe threat, but and isolated storm may occasionally grow stronger. The main concern will be for slow-moving storms capable of producing very high rainfall rates to slowly move, causing localized concerns for flooding. Overall, though, the forecast is for more summer weather to continue, typical for summer.
Hydrology
Issued at 300pm EDT Wednesday August 21 2024
Post-Debby, rainfall coverage has been more limited. However, portions of Manatee and Sarasota County remain heavily saturated after record rainfall associated with Debby. Even outside of this area, soils are still on the relatively saturated side; and the current forecast continues to favor additional rainfall in the days to come. Daily PWATs (Precipitable Waters) are expected to be near climatological max values, and certainly above the 90th percentile. With light flow and deep moisture, this favors efficient rainfall rates and slow moving storms. Under these conditions, it will be more difficult for water to drain, leading to a greater chance for mainly aerial flooding as opposed to flash flooding. However, urban areas with poor drainage could see additional localized impacts.
Water levels are also likely to continue rising on area rivers as additional rainfall occurs. Several are currently in action stage, and minor flooding is also forecast on several rivers, including the Manatee River near Myakka Head, Little Manatee River near Wimauma, Horse Creek near Arcadia, Myakka River at Myakka River State Park, and even the Withlacoochee River at Trilby. The official forecasts for all rivers do not show impacts beyond minor flooding at this time; and NAEFS (the 10-day ensemble forecasts) generally support this trend as well. The forecast point with the least confidence is the Myakka River at Myakka River State Park. There is a large spread in the ensemble members into next week, with the possibility of moderate flooding not completely out of the question (although a low probability outcome at this time). However, the most-likely scenario still shows the river gradually declining next week.
Sea Breeze Thunderstorm Regime For Thursday: 4 Sea Breeze Thunderstorm Regime For Friday: 6
For additional information on sea breeze regimes, go to: https://www.weather.gov/tbw/ThunderstormClimatology
NOAA Tampa FL Office: Watches - Warnings - Advisories
FL...None. Gulf waters...None.
