textproduct: Jacksonville

KEY MESSAGES

For the latest NE FL and SE GA Daily Key Messages please visit: https:/www.weather.gov/media/jax/briefings/nws-jax-briefing.pdf

- Coastal & Marine Hazards Continue through the Weekend. Small Craft Advisory Tonight through Saturday. High Rip Current Risk, Rough Surf, Elevated Tides and Beach Erosion.

- Minor to locally Moderate Tidal Flooding Continues for the St Johns River through the weekend. Coastal Flooding along the Atlantic coast will fall below Minor Flood levels this evening before increasing again Friday.

- Hurricane Isaias expected to track northward through the Gulf and make landfall in the Florida Panhandle Friday night. Strengthening Onshore Winds and Additional Periods of Heavy Rain Friday Friday and Saturday are expected.

- Scattered thunderstorms with isolated severe potential Saturday afternoon and evening.

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Coastal and Marine Impacts Continue, Including Coastal Flood Warning for Upstream St. Johns River

- Numerous showers across North Central FL decreasing in coverage northward Nearly stationary boundary remains draped just south of our region, and has been generally nudging further southward throughout the day today as high pressure ridging is trying to make more of a push from our north. Main impact today will be more of a presence of drier air across southeast GA and to a small extent over northeast FL, which can already be seen on satellite imagery with breaks in the persistent low clouds. With onshore flow continuing just north of the front, showers with occasional heavy rainfall and perhaps a few rumbles of thunder will continue across a large portion of the area today similar to yesterday. The main difference being the highest PoPs and potential for heavy rainfall/flooding will shift slightly southward with the front, with generally from Saint Augustine to Gainesville and areas south being the primary impact zone. Showers will be more isolated near the I-10 corridor today, which is good news for Duval County where some areas have received 4-8+ inches of rain over the past 24 hours.

Aside from rainfall and breezy onshore winds, the other primary impact continues to be coastal/marine/St. Johns River flooding, with Coastal Flood Advisories continuing for the entire coast and St. Johns River east of Downtown JAX to Mayport, where about 1-1.5 feet of water above normally dry ground is expected at times of high tide. South of the JAX area, opted to upgrade to a Coastal Flood Warning based on trends and other ground truth, as water levels near or just above 2 feet above normally dry ground is forecast, and has already occurred in a few areas. This threat is expected to continue through at least Thursday Morning's high tide. Rip current risk also continues to be high at all area beaches.

Drier air will only make it to about the FL/GA border tonight before a shift in the pattern is expected Thursday onward (more on that below), which will also suppress coastal showers just a bit overnight. Chances will mainly be confined to similar areas as during the day today, but overall around 10-20% less.

With breaks in the sun today, especially across southeast GA, these areas will see temps a few degrees higher than average. Generally looking at low 80s over inland GA and the upper Suwannee Valley area, and mid 70s to around 80 elsewhere.

SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/

Main Highlights This Period:

- Heavy downpours and flash flood risk returns Friday and Saturday

- Isolated severe thunderstorms potential Saturday afternoon for inland areas.

- Strong onshore winds renew the surf zone risk and continue tidal flooding within the St Johns River and along the Atlantic coast.

An old stalled frontal boundary will gradually be lifted northward as a warm front across northeast FL through Friday as low-level southerly flow between Hurricane Isaias and the Bermuda ridge intensify. Deep tropical moisture will lift northward with the boundary on Friday as well, renewing the threat for heavy downpours and flash flooding Friday and Saturday. Though it will depend on the warm fronts northward progress, it appears that the only zones that may support thunderstorm development will be south of I-10; however, this may change in response to any changes in the intensity of Hurricane Isaias as it approaches the northern Gulf coast. Highest concerns for flooding will be focused along the I-95 corridor and beach communities on Friday.

By Saturday the warm front is expected to flex as it pushes toward the Altamaha river by Saturday afternoon. Strong influx surface moisture south of the front will help destabilize conditions Saturday afternoon. Given the low level wind shear and sufficient instability, severe thunderstorms are expected to develop and potential tap into the available low-level helicity. Per the latest guidance, the boundary layer storm- relative helicity may support the potential for isolated tornadoes for inland areas of southeast GA and south into the Suwannee River Valley during the afternoon and evening hours Saturday.

Remnants of hurricane Isaias will drift well to north into the Appalachians by Sunday as it becomes extratropical in nature. A steady stream of deep moisture on southwesterly flow will keep airmass unstable, supporting scattered to numerous thunderstorms ahead of the developing cold front trailing behind the remnant tropical low. Though a few strong thunderstorms may develop Sunday, severe thunderstorms appear unlikely with a weaker and unidirectional low level wind profile.

In addition to the heavy rain/flood and severe thunderstorm potential, strong onshore winds through Saturday will prolong the coastal flooding along the Atlantic coast/St Johns River, deadly rip current/surf, and marine hazards through the weekend.

Temperatures will warm back into the 80s through the weekend and perhaps approach 90 degrees for portions of NE FL by Sunday as sunshine makes a return to the area.

LONG TERM /MONDAY THROUGH WEDNESDAY/

Main Highlights This Period:

- Warmer than normal

- Northeasterly Wind Surge late next; Elevated tidal flooding possible

The cold front trailing the remnants of Isaias will push in from the northwest through the first half of Monday, with high pressure building in from the west behind it. Dry northwest flow in the wake of the front will scour out the remaining moisture, leading to rain- free, mostly sunny, and seasonably warm conditions through most of next week. Offshore flow and decreasing tidal levels are expected next week; however, a dry backdoor front will bring another surge of northeasterly winds to the coast and potentially elevate tidal levels again toward the end of next week.

AVIATION /06Z THURSDAY THROUGH 06Z FRIDAY/

The 06Z TAF period will begin with predominantly MVFR CLNGs along the coast and CRG and JAX with IFR CLNGs developing at GNV and VQQ through 09Z with near calm winds inland and 5-8 knots along the coast. Showers may move onshore at times after 09Z at SGJ with VCSH otherwise noted there.

Thursday, VFR ceilings should largely return to the TAF sites after 15Z/16Z while IFR ceilings will lift to MVFR by 15Z at GNV, then to VFR by after 17Z. Northeast winds will continue to be 10-15 knots along the coast with gust near 20 knots due to onshore flow between high pressure northeast of the region and a frontal boundary to the south. Drier air from the north will limit showers chances at SSI while coastal showers will be most likely at SGJ. Have kept PROB30 groups at CRG and VQQ where the northern boundary of heavier coastal showers will be nearest in the afternoon with coastal showers more president at SGJ today. Winds will become more easterly after 00Z with showers again persistent at SGJ where MVFR CLNGs will return along with GNV.

MARINE

Decreasing east northeast winds and seas early this morning with caution conditions for the offshore waters through late this morning due to a briefly weakening gradient between high pressure to the north and northeast of the waters and a frontal boundary south of the waters. The front will lift northward through the waters starting tonight with another high pressure center building in north of the region Friday and to the north northeast on Saturday. Small Craft Advisory conditions will return due to elevated easterly winds and seas Friday through Saturday.

The National Hurricane Center is monitoring Hurricane Isaias in the southwestern Gulf. This system is expected to move northward towards the central Gulf coast region Friday into Saturday. Showers and thunderstorms will increase in coverage throughout our local waters during the weekend as tropical moisture surges northward on the eastern periphery of this tropical system.

Rip Currents: A northeasterly wind surge persisting along the Georgia and northeast FL coast through today will result in strong rip currents and rough surf. High Risk for Rip Currents will likely continue through this weekend with continued breezy onshore flow.

FIRE WEATHER

A brief break in the rain today for most areas, followed by a return to soggy conditions Friday and increasing thunderstorm chances over the weekend as a warm front lifts across the region. Direct local impacts from Hurricane Isaias are not expected but fringe outer rain bands may reach portions of the Suwannee Valley Friday night into Saturday. Conditions will dry out and warm up next week as drier air pushes in behind the remnants of Hurricane Isaias. No immediate fire weather concerns or weather watchouts over the weekend.

FOG POTENTIAL AND OTHER WEATHER REMARKS: Dense fog formation is not expected over the next few days. Heavy rainfall may lead to another potential period of flash flooding Friday and Saturday. Isolated severe thunderstorms will be possible Friday night through Saturday with risk of isolated tornadoes.

HYDROLOGY

Portions of the St Marys, Satilla, and tributaries to the St Johns River have risen into minor or moderate flood stage in response to widespread 4 to 8 inch rainfall over the portions of those basins over the last several days. Additional rainfall through the weekend may prolong or lead to other local river rises. Rain-free conditions next week will allow river levels to lower.

TIDES/COASTAL FLOODING

Coastal flooding will persist through the weekend within the St Johns River. Tides will be elevated along the Atlantic coast this morning but will lower as winds continue to decrease this afternoon. Winds will strengthen through Friday and combine with the astronomical peak tides with the New Moon, yielding Minor to low-end Moderate flooding along at the beaches through at least Saturday night's high tide.

Due to widespread 4 to 8 inches of rainfall across the lower basin of the St Johns river, tidal levels will likely reach moderate levels again with the morning high tide, up to 2.25 feet above normally dry ground. A Coastal Flood Warning remains in effect due to the combination of the freshwater runoff and ongoing 'reverse flow' with the middle and upper portions of the St Johns River. Will reassess the need to extend the Coastal Flood Warning later this morning after high tide. Anticipate water levels at high tide to be at least at Minor Flood level through the weekend within the St Johns.

PRELIMINARY POINT TEMPS/POPS

AMG 82 68 77 69 / 0 10 50 80 SSI 83 73 82 74 / 20 30 60 90 JAX 82 71 81 72 / 50 40 70 90 SGJ 81 73 82 74 / 80 60 90 90 GNV 80 69 81 71 / 70 60 90 60 OCF 79 70 83 73 / 90 70 80 40

JAX WATCHES/WARNINGS/ADVISORIES

FL...Coastal Flood Advisory until 5 PM EDT this afternoon for FLZ124-138-233-333. High Risk for Rip Currents through late Saturday night for FLZ124- 125-138-233-333. Coastal Flood Advisory until 2 PM EDT Saturday for FLZ125-225. Coastal Flood Warning until 5 PM EDT this afternoon for FLZ132- 137-325-633. Coastal Flood Advisory from 5 PM this afternoon to 2 PM EDT Saturday for FLZ132-137-325-633. GA...Coastal Flood Advisory until 5 PM EDT this afternoon for GAZ154-166. High Risk for Rip Currents through late Saturday night for GAZ154- 166. MARINE...Small Craft Advisory from 8 AM Friday to 2 AM EDT Sunday for AMZ450-470. Small Craft Advisory from 2 AM Friday to 2 AM EDT Sunday for AMZ452-454-472-474.