A frontal boundary sliding into the Southeast will begin to enhance thunderstorm activity across North Florida late Thursday and Friday, then potentially produce more widespread rain and thunder across portions of Central and South Florida Saturday and Sunday.

The storm system might also acquire tropical characteristics as it moves offshore into the Atlantic Ocean by early next week.

Thunderstorms capable of producing wind damage, small hail and waterspouts are possible just ahead of the front Thursday evening in northeast Florida, then again Friday across a large section of North and Central Florida.

The Storm Prediction Center placed a small section of Northeast Florida under a "marginal risk" (level 1 out of 5) for wind damage Thursday afternoon and evening.

Friday's afternoon and evening storms will be moving unusually fast for this time of year, with clusters of activity propagating in generally a north-to-south fashion, along with some backing to the southwest. Here are Friday's most likely arrival times for the storms in a few select cities or regions:

Lake City, Jacksonville: 4 to 7 pm
Gainesville, Ocala, Orlando: 5 to 9 pm
Space and Treasure Coasts: 6 to 10 pm
Nature Coast, Lakeland, Tampa: 7 to 11 pm

The storm coverage Saturday will be more focused in Central Florida as the front continues to slide south, although the cells likely won't be as strong or as widespread since the front will be weakening. The greatest concentration of Saturday's storm activity will be near and just south of a line from Tampa to Melbourne, sliding down into portions of South Florida by the early evening. Drier air behind the boundary will keep rain chances lower than normal Saturday across much of North Florida and in the Panhandle.

The weakening front is expected to stall across South Florida Sunday, where numerous showers and thunderstorms are also likely to develop by the afternoon and evening hours, generally speaking from Naples to Miami. Higher-than-normal rain chances will also exist Sunday in the Florida Keys, whereas much of North and Central Florida will be behind the front and largely rain-free.

NEW DEVELOPMENT POSSIBLE
NHC: Medium chance of tropical development in next five days.

The frontal boundary sagging across Florida this weekend is tied to a larger area of low pressure that is forecast to move into the Atlantic Ocean early next week, where the National Hurricane Center says there's a "low chance" it could acquire enough tropical characteristics to become a tropical depression or storm in the next five days. If this were to occur, long range forecast data suggests upper-level winds might be too strong or chaotic to allow it to become very organized. However, weak steering currents might eventually allow the system and its associated moisture to drift back in the direction of Florida later in the week.

Expires at 2:00pm on Friday July 23rd, 2021

Deeper moisture is back on the move into Florida this week, making way for numerous thunderstorms to replace the recent stretch of drier weather over the next few days across most of the state.

A slow-moving front drifting through the Southeast is forecast to induce a more dominant southwesterly wind, drawing deeper moisture into the atmosphere from the Gulf of Mexico toward the front. The moisture will intersect the lift from the nearby front in the Florida Panhandle and along the I-10 corridor from Tallahassee to Jacksonville, which is where showers and thunderstorms will be most widespread through midweek.

A second area of higher rain chances will develop this week along a progressive Gulf Coast sea breeze that will likely trigger broken lines of cells on its journey inland each afternoon. Where this boundary interacts with a pinned Atlantic Coast sea breeze is where stronger and more numerous storms could develop by the early evening hours, which will likely be near and just west of the the I-95 corridor from Jacksonville to Miami, including the Orlando metro area.

This type of pattern generally leads to drier weather immediately along the Gulf Coast from Florida's Big Bend to Tampa, including areas along the Nature Coast and near or west of I-75 in North and Central Florida. The added cloud cover from the more widespread thunderstorm activity also tends to limit afternoon heating and reduce daytime highs, which is also in the forecast for most Florida cities. The deeper moisture and stalled front is forecast to linger across much of Florida through at least Thursday, before the front weakens and higher pressure builds in Friday or Saturday.

NEW DEVELOPMENT POSSIBLE
NHC: Medium chance of tropical development in next five days.

Expires at 8:00pm on Monday July 19th, 2021

Florida is no stranger to strong afternoon thunderstorms in July, but they’re likely to be more widespread than usual Monday afternoon and evening.

The greatest risk for widespread thunderstorms is over west-central Florida, centered on the Tampa/St. Pete metropolitan area. However, these strong storms may also occur as far south as the Fort Myers area and as far north and east as the Orlando, Gainesville, and Jacksonville areas. Scattered thunderstorms are likely over the Big Bend and Panhandle areas, but widespread severe weather is somewhat more unlikely in those areas.

A combination of several factors are contributing to the strong thunderstorm potential: an upper-level trough near the Atlantic coast is forecast to move westward over the state and a moist southeasterly wind pattern will tend to focus the sea breeze storms over the western half of the peninsula. Cool air high in the atmosphere from the trough will move over top of the typically warm, humid, and unstable air mass over the state, which will contribute to the risk for hail and damaging gusts from the strongest storm clusters.

Areawide rainfall is expected to average around an inch, focused on the western half of the peninsula, but more localized torrential rain is highly probable. Rainfall over the past month is running twice to nearly three times the average from Interstate 4 northward into the Ocala, Gainesville, and Lake City areas. As little as 2 to 3 inches of rain in one hour may trigger flash flooding from Lee county northward to Tampa and toward Gainesville. These communities received heavy rain from Tropical Storm Elsa last week. Frequent lightning, as always, poses a concern. Lightning can strike in areas where it is not raining, which may cause those outside off guard.

The first storms are likely to develop along or west of Interstate 95 on the east coast around or shortly before noon. They will reach the Fort Myers and Naples area early Monday afternoon. The Orlando area is on track to see the strongest storms during the early and mid afternoon hours of Monday, spreading to the Tampa and St. Pete areas mostly after 3 o’clock before moving into the Gulf around sunset. A similar pattern is likely over the northern peninsula: storms in the Jacksonville to Daytona areas in the early afternoon will reach Interstate 75 during the mid to late afternoon and finally to the Nature Coast by early evening.

Heavy rain and flash flooding may result from storms in the Big Bend and Panhandle, too. The storms along the sea breeze should develop around 1 o’clock and spread northward to the Georgia and Alabama state lines shortly before 4 o’clock. Conditions have been wetter than normal over most of the spring, especially over the western Panhandle, and from Tropical Storm Claudette in June.

A similar pattern is on tap for Tuesday. The greatest concentration of thunderstorms is likely over the interior of the Florida Peninsula during the early afternoon and then favoring the west coast later in the afternoon and early evening hours. There are signs some drier air from the east may limit the number of storms Thursday or Friday.

LOCATED 90 MI ENE OF BOSTON MASSACHUSETTS
MOVING NE AT 35 MPH
WINDS 50 MPH
PRESSURE 999 MB

LOCATED 10 MI WSW OF MONTAUK POINT NEW YORK
MOVING NE AT 31 MPH
WINDS 50 MPH
PRESSURE 1000 MB

LOCATED 90 MI SW OF MONTAUK POINT NEW YORK
MOVING NE AT 31 MPH
WINDS 50 MPH
PRESSURE 1000 MB

LOCATED 5 MI E OF ATLANTIC CITY NEW JERSEY
MOVING NE AT 31 MPH
WINDS 50 MPH
PRESSURE 1000 MB

LOCATED 45 MI SW OF LEWES DELAWARE
MOVING NE AT 25 MPH
WINDS 50 MPH
PRESSURE 1002 MB

LOCATED 50 MI NNW OF NORFOLK VIRGINIA
MOVING NE AT 25 MPH
WINDS 50 MPH
PRESSURE 1002 MB

LOCATED 65 MI W OF NORFOLK VIRGINIA
MOVING NE AT 21 MPH
WINDS 50 MPH
PRESSURE 1004 MB

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