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 through Tonight, again Friday and Saturday. High Rip Current Risk, Rough Surf, Elevated Tides and Beach Erosion. Minor Tidal Flooding Continues for the St Johns River through the Weekend

- Tropical Storm Isaias Developed early this morning. Strengthening Onshore Winds and Additional Periods of Heavy Rain Friday and

UPDATE

Scattered thin bands of coastal showers continue to move onshore portions of the SE GA coast from near Fernandina Beach northward to Cumberland Island and also the Northeast FL coast south of Fernandina Beach to the JAX beaches and Mayport and St Augustine Shores and across Flagler Beach and Palm coast while steadier light to moderate showers persist over north central FL just north of the frontal boundary currently over central FL.

A gradual decrease in showers is expected overnight with occasional coastal showers moving onto the NE FL coast and scattered to numerous showers remaining over Marion and Flagler counties where another half inch of rain is expected with a quarter inch over the NE FL coast and less than quarter inch over much of inland NE FL north of Gainesville. Winds will stay 10-15 mph at the coast, with inland winds decreasing from 5-10 mph to 3-6 mph after midnight. Mostly cloudy skies will remain along and north of I-10 with partial clearing at times over inland SE GA where very light winds will help support some patchy fog while low stratus over inland NE FL may also settle near the surface with reduced visibility late tonight towards sunrise. Temperatures now in the mid to upper 70s now will slowly fall to the low 70s along the coast and cool into the upper 60s to near 70 over inland NE FL and the mid 60s over inland SE GA.

This evening high tide cycle has peaked between 1.70 to 2.20 ft MHHW (Mean Higher High Water) along the coast and is now shifting through the St Johns river in eastern Duval into downtown JAX, but obs and guidance continue to support the existing Coastal Flood Advisory for the coast and Coastal Flood Warning along the river from downtown southward to Lake George.

NEAR TERM /THROUGH TONIGHT/

Main Highlights Today and Tonight:

- Flood Threat from Heavy Downpours Continues Today for Coastal Northeast FL and Camden County, GA

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

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 /THURSDAY NIGHT THROUGH FRIDAY NIGHT/

Main Highlights This Period:

- Heavy rainfall potential Thursday in North-Central Florida, expanding northward through Friday

- Onshore winds strengthening through Friday, increasing surf zone risk and continue tidal flooding within the St Johns River and along the Atlantic coast.

An uneven stalled frontal zone will be situated across central FL through the end of the week. The position of the front and a wave of low pressure developing off the eastern FL coast will continue to bring gusty winds along the coast through the end of the week. Dry air will limit rain chances north of I-10 through Thursday before steering flow turns more southerly by Friday, allowing for deeper moisture to gradually lift northward with the developing warm front. Influence from Tropical Cyclone Isaias is expected for Friday while the pressure gradient tightens between the storm and an area of high pressure along the Mid Atlantic. Strengthening onshore flow will likely result in rough surf conditions, rip currents, and continue a 'reverse flow' with elevated tides in St Johns River and intracoastal waterway.

After a slight "break" in the soggy conditions Thursday, the potential for training downpours off the Atlantic may result in the consideration of Flood Watches for coastal areas on Friday.

Hurricane Isaias path is expected to make a turn to the north and push toward the northern Gulf Coast. At this time, the main impacts are expected to be additional heavy rain potential Friday where the Weather Prediction Center already has a "Marginal" (5%) risk of flash flooding.

Not much change in the temperature ranges to end the week with abundant cloud cover keeping afternoon highs generally in the upper 70s to low 80s while overnight lows will be in the upper 60s and low 70s.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Main Highlights This Period: fri-mon

- Flood risk and strong to severe thunderstorm risk on Saturday as Tropical Cyclone Isaias lifts north across the Gulf coast.

Strong southerly flow in response to the fast-moving tropical storm moving northward into the lower Mississippi region this weekend will result in warming temperatures and destabilizing airmass this weekend as the pseudo warm front lifts across the region.

As a result of the storm trajectory of Tropical Storm Isaias, it is possible that the pseudo warm front evolving with the passing system as it undergoes extratropical transition may hang up across the region on Saturday. Forecast soundings and hodographs do indicate low level veered flow, which may favor some organized thunderstorms embedded along the fringe bands of Isaias. Being in the dynamically favored quadrant, a few organized thunderstorms and potential tornadoes can develop Saturday afternoon. Additionally, the deep tropical moisture and heavy rain rates and wet antecedent conditions will likely yield a flood risk through the weekend as well.

Next week, a trailing cold front behind the remnant tropical low will push across the area bringing dry weather, clearing skies, and warmer temperatures.

AVIATION /00Z THURSDAY THROUGH 00Z FRIDAY/

The TAF period will begin with predominantly MVFR CLNGs at all sites with northeast winds around 10 knots at the coast and decreasing to 5-8 knots inland. The MVFR ceilings will lower to IFR levels at the inland sites from 05-09Z at GNV, VQQ, and JAX with MVFR VSBY inland as winds lessen under 5 knots and low stratus attempts to lower near the surface. A few showers will continue to move onshore the Northeast FL coast inland to CRG and JAX at times overnight with brief IFR ceilings associated with showers at SGJ, CRG, and JAX with diminished chances inland at GNV and VQQ after 09Z.

Thursday, VFR ceilings should largely return to the TAF sites after 15Z except at SGJ, 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 a PROB30 group at CRG where the northern boundary of heavier coastal showers will be nearest in the afternoon.

MARINE

Small Craft Advisory conditions persist this evening with elevated winds and seas over the waters as weak low pressure off the east central Florida coast moves slowly eastward tonight and Thursday maintaining breezy northeasterly winds. Onshore winds may briefly decrease Thursday before strengthening back to Small Craft Advisory levels by late Friday as high pressure builds in again over the Mid-Atlantic states and wedges down the southeastern seaboard. The National Hurricane Center is monitoring Tropical Storm 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 tonight 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

- Areas Of Low Daytime Dispersions Inland Ne Fl Today

Soggy conditions will limit fire weather concerns. Strong northeast winds will persist and gradually shift easterly through the end of the week with gusts strongest at the coast, up to 35 mph at times. Limited mixing due to thick overcast will keep smoke dispersion low to poor through the rest of the week and likely into the weekend. Due to elevated coastal winds, high overnight dispersions are expected. Waves of heavy rain will become focus south of I-10 Thursday, expand northward into southeast GA Friday. Increasing potential for thunderstorms this weekend as Hurricane Isaias tracks northward into the Gulf coast.

Fog Potential: Heavy rainfall combined with saturated soils will likely produce localized flash flooding along the coast today. Dense fog formation is not expected over the next few days.

HYDROLOGY

The Flood Watch has been cancelled earlier today as rainfall coverage has diminished greatly across Northeast FL and the coast where heavier totals occurred on Tuesday and Tuesday evening.

Portions of the St Marys, Satilla, Santa Fe and Alapaha Rivers have risen into minor flood stage in response to widespread 4 to 8 inch rainfall over the last several days. However, most locations are not expected to rise into flood over the next several days due to the dry conditions and low water levels prior to this recent bout of heavy rain. With a break in the heavy rain over the next few days, river levels are expected to gradually lower below flood.

TIDES/COASTAL FLOODING

A Coastal Flood Advisory remains in effect through tonight for the Atlantic Coast while the Coastal Flood Advisory within the St Johns River system was extend through the Saturday Morning high tide. Reverse flow within the river is likely to raise tidal levels to 1.75 to 2.25 feet above normally dry ground at times of high tide through the end of the week. Given the 3 to 6 inches of freshwater rainfall over the last 24 hours, it's possible that runoff will exacerbate tidal flooding with this morning's high tide (7-10 AM) within the mouth of St Johns River to near Moderate Levels.

PRELIMINARY POINT TEMPS/POPS

AMG 64 83 67 77 / 0 10 10 50 SSI 73 82 73 82 / 20 40 30 70 JAX 71 83 71 80 / 40 50 40 80 SGJ 73 82 73 82 / 70 80 50 90 GNV 70 81 70 81 / 80 80 40 90 OCF 70 81 70 83 / 90 100 50 90

JAX WATCHES/WARNINGS/ADVISORIES

FL...Coastal Flood Advisory until 5 PM EDT Thursday 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 Thursday for FLZ132-137- 325-633. Coastal Flood Advisory from 5 PM Thursday to 2 PM EDT Saturday for FLZ132-137-325-633. GA...Coastal Flood Advisory until 5 PM EDT Thursday for GAZ154-166. High Risk for Rip Currents through late Saturday night for GAZ154- 166. MARINE...Small Craft Advisory until 2 AM EDT Thursday for AMZ450-452- 454-470-472-474.