What the forecast actually says — NWS Area Forecast Discussions, decoded into plain English.
Area Forecast Discussion · National Weather Service Jacksonville (JAX) · issued Friday, September 11 at 8:53 AM EDT.
Revised in 14 passages since the 2:54 AM discussion. See every revision.
Messages
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Numerous Afternoon and Evening Thunderstorms Expected through Saturday. Strong Storm Potential Along the I-95 Corridor During the Late Afternoon Hours. Stronger Storms May Produce Wind Gusts of 40-55 mph, Frequent Lightning Strikes, and Torrential Downpours that Could Result in Localized Flooding.
Daily Peak Heat Index Values of 104-108 Degrees Expected. through Monday.
Moderate Rip Current Risk Continues at All Area Beaches through Monday. High Risk Likely from Tuesday through Thursday of Next Week.
Short Term
Potential for strong thunderstorms and localized flooding this afternoon and evening, especially along the I-95 corridor.
Moderate Rip Current Risk at All Area Beaches.
Mean layer ridge oriented more or less west-east through 700 mb is located in central FL area. Typically for September this ridge is located further north. Deep layer flow is southwesterly at about 10 knot, and we continue with the deep moisture in place with the 18z JAX Sounding showing 2.29 inches and 500 mb temp of only -4.1C. Fairly confident PWATS will stay the same today, but the 500 mb temperatures may drop another degree or so during the day. Models suggest that some shortwave energy may impinge on the forecast area after 21z today which will likely encourage more cloudiness and probably boost rain chances this evening.
Given the moisture and summer-like pattern, we anticipate scattered to numerous showers and storms to develop during the day. Initial develop of convection likely to be around any lingering boundaries from Thursday, and along the west and east coast sea breezes that develop by the early afternoon. Climatology would suggest the I-75 corridor first, though, near the developing west coast sea breeze. The movement of the west coast sea breeze may meet the east coast sea breeze this afternoon and early evening, and cells mergers may would be near and east of the U.S. Highway 301 area. The moisture laden airmass will be efficient for heavy rainfall/localized flooding. Rain amounts in excess of 3 inches in spots are likely. The DCAPE on the model soundings looks unimpressive at about 500-600 J/kg, similar to yesterday, so for now assuming peak thunderstorm gusts of about 40-50 mph. Cannot totally rule out an isolated severe storm though where strongest convergence occurs.
Daytime highs will be in the lower 90s, and probably around 90 at the east coast as the sea breeze develops. Heat index values will hover under Heat Advisory criteria, with values in the 104-108 F range. Lows tonight in the lower to mid 70s.
Short Term
Potential for strong thunderstorms and localized flooding on Saturday afternoon and evening, especially along the I-95 corridor.
Scattered to numerous showers and storms are anticipated on Saturday as moist southwesterly flow, with precipitable water values of 2 to 2.3 inches, continues to move over the region from out of the Gulf. There is a potential for heavy rains and localized flooding for storms developing along the sea breeze boundaries and areas of convergence, likely along and west of the I-95 corridor. Convection is expected to be less widespread on Sunday as the high pressure ridge shifts northward and crosses over the forecast area, with the prevailing flow gradually shifting to a more northeasterly onshore flow by the beginning of next week. High temperatures will rise up into the lower 90s this weekend with overnight low temperatures dropping down into the lower to mid 70s over inland areas and int the mid to upper 70s for areas along the coast. Heat index values today will rise to over 100 with apparent temperatures potentially reaching as high as 110 for northeast Florida, however conditions are anticipated to remain below heat advisory criteria. Potential for patchy early morning fog and low cloud decks over inland areas before and around sunrise during the overnight and early morning hours this weekend.
Long Term
Main Highlights This Period Monday through Thursday:
Daily Thunderstorms Potential Each Day Next Week.
High Rip Current Risk Develops on Tuesday and Continues through at Least Thursday Next Week.
Northeasterly onshore flow will be in place through the latter part of next week as the axis of high pressure rotation settles in to the north. Chances for daily bouts of showers and storms will lessen for southeast Georgia and areas of northeast Florida north of the I-10 corridor as drier air advects into the forecast area from out of the northeast, with a higher likelihood of convection for areas south of I-10. Above average high temperatures reaching into the lower 90s will gradually drop down into the upper 80s and be nearer the seasonal average by midweek. Heat index values will drop down to be below 100.
Rip current risk will also become elevated rather than moderate as a result of the pattern shift.
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