301 FXUS62 KJAX 120750 AFDJAX Area Forecast Discussion National Weather Service Jacksonville FL 350 AM EDT Mon Aug 12 2019 ...HOT AND HUMID AGAIN TODAY WITH HEAT INDICES PEAKING NEAR 106-112... ...LOCALLY HEAVY RAINFALL LATE THIS AFTERNOON AND EVENING EXPECTED NEAR THE I-75 CORRIDOR... .NEAR TERM...Today and Tonight... Similar story, different day. Oppressive heat is expected by noon and through most of the afternoon as thunderstorms eventually develop and provide relief. While marginal in some areas, decided to issue the heat advisory for the whole area once again until 6 PM. With the sea-breeze boundaries moving inland, scattered showers and thunderstorms will help provide relief to some areas fairly early in the afternoon. The longest duration areas observing heat advisory conditions will most confidently be across the Suwannee Valley and into SE Georgia where precipitation will be fairly isolated and temperatures rise into the mid and upper 90s. With precipitation becoming more widespread by 3-4 PM, much of the advisory area in NE Florida will probably be below criteria. Regardless, it has been observed by numerous stations that even after the sea-breeze passes, the combination of slightly cooler temperatures but higher surface dewpoints still realizes heat advisory worth conditions. True relief will come where convective activity occurs. Surface flow is very weak today so the east coast sea-breeze moves inland by early afternoon, initiating a few scattered showers and thunderstorms. Additional convection develops along the Gulf Coast sea-breeze and slowly moves inland. Mesoscale models are all in fairly good agreement that these boundaries merge along the I-75 corridor by late afternoon. With dewpoint temperatures in the mid to upper 70s, and air temperatures in the mid 90s, CAPE values are once again expected to be very high, despite warm temperatures aloft. Convective activity associated with the merging boundaries likely continues into the evening hours across the Suwannee Valley and into portions of SE Georgia before eventually fading. A few strong storms will be possible with the merging boundaries, but heavy rainfall remains the main concern. GOES derived PWATs suggest 2.3-2.7 inches present over the I-75 corridor. Isolated showers dissipate overnight with partly cloudy skies by Tuesday morning. .SHORT TERM...Tuesday and Wednesday... By Tuesday, the upper level ridge axis begins to stretch more east to west versus the more amplified north to south setup that has persisted for multiple days. A wedge of drier air pushes into the northern zones, limiting coverage across SE Georgia. Further south, sufficient moisture remains, likely leading to another round of showers and thunderstorms, mostly driven by the sea- breeze boundaries moving inland. Temperatures are still warm aloft (500 mb temps -3 to -4) so expect late initiation with activity continuing into the evening hours as mesoscale boundaries collide. Ridge axis directly overhead on Wednesday with as a shortwave trough descends through the Midwest. The frontal boundary associated with the trough is expected to be north of the area, limiting convection to the diurnal processes that are typical this time of year. Precipitation coverage will be slightly higher on Wednesday with the drier air offshore. Temperatures closer to climatological normals for NE Florida (low 90s) during the short-term however, SE Georgia still 3-5 degrees above normal (mid to upper 90s). Dewpoint temperatures in the mid to upper 70s keep heat index values elevated with some areas possibly reaching heat advisory criteria, especially across SE Georgia. .LONG TERM...Thursday through Monday... With the shortwave trough digging into the Southeast, the more amplified pattern of a ridge to the west and a weak trough over the region resumes, especially below 300mb. With the trough positioned slightly west of the region, a deep tropical airmass continues to persist over the area. This favors numerous showers and thunderstorms throughout the long-term period. Models attempt to organize areas of vorticity along the stalled boundary, but all that would be expected if something were to form would be enhanced rainfall. Temperatures finally drop to near normals with the trough breaking down the upper level ridge. Low 90s are forecast throughout the long-term. && .AVIATION... Possible low cigs and vsby this morning mainly for GNV and VQQ due to recent rainfall. Otherwise VFR cigs look to prevail today for the TAFs with a good chance of showers and storms, with GNV having the best shot of seeing convective impacts at the terminal. For now, have included TEMPO group for them 18z-22z for MVFR and gusty winds, with rest of the TAFs mentioning VCTS. Winds will be light and variable early today, then becoming easterly in the aftn near 8-12 kt, with exception at GNV where more southerly flow at 5-10 kt is expected. && .MARINE... Weak flow across area waters continues to provide shallow sea levels and below criteria winds. Winds do approach caution levels for off shore waters toward Wednesday evening as a trough of low pressure moves into the Southeast. The pressure gradient relaxes toward the end of the week with winds decreasing to 10-15 knots. Rip Currents: Moderate risk for all area beaches due to onshore flow during the afternoon, coupled with a lingering swell. && .PRELIMINARY POINT TEMPS/POPS... AMG 96 74 96 76 / 10 10 20 10 SSI 90 78 91 79 / 20 0 10 10 JAX 93 77 93 77 / 30 10 20 20 SGJ 91 76 90 76 / 20 10 30 20 GNV 93 76 92 76 / 60 70 60 30 OCF 92 76 90 75 / 60 60 60 40 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...Heat Advisory from noon today to 6 PM EDT this evening for Baker- Bradford-Central Marion-Clay-Coastal Duval-Coastal Flagler- Coastal Nassau-Coastal St. Johns-Eastern Alachua-Eastern Marion-Gilchrist-Hamilton-Inland Duval-Inland Flagler- Inland Nassau-Inland St. Johns-Northern Columbia-Putnam- Southern Columbia-Suwannee-Union-Western Alachua-Western Marion. GA...Heat Advisory from noon today to 6 PM EDT this evening for Appling-Atkinson-Bacon-Brantley-Clinch-Coastal Camden- Coastal Glynn-Coffee-Echols-Inland Camden-Inland Glynn-Jeff Davis-Northeastern Charlton-Northern Ware-Pierce-Southern Ware-Wayne-Western Charlton. AM...None. && $$ McGinnis/Shashy/