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

- Heavy rainfall and freshwater flooding possible along the I-95 corridor in NE FL through today.

- Local nor'easter conditions continue: Rip Currents, Rough Surf, Minor Tidal Flooding; Prolonged tidal flooding likely within the St Johns River through the Weekend.

- Tropical Depression Nine in the Gulf of America is forecast to move toward the northern Gulf coast Friday night, intensifying into a hurricane as it does so. Uncertainty in track continues. Current Local impacts are expected to be additional heavy rain and potential for flash flooding.

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 as Breezy Onshore Winds Persist at Coastal Locations.

A weak wave of low pressure in the NE Gulf will move eastward across the stationary frontal boundary draped across central FL into the Atlantic this morning. Breezy NE winds continue today with the low pressure off the coast of east-central FL and high pressure over the Mid-Atlantic wedging down the southeastern seaboard. Drier air (PWATs 1-1.5 in) continues to advect into inland southeast GA keeping rain chances to areas mainly south of Waycross where deep tropical moisture remains. Mostly stratiform rainfall continues in the moist air mass with rounds of convergent bands shifting onshore bringing heavier downpours to the Atlantic coast, I-95 corridor and St Johns river basin. A Flood Watch remains in effect for coastal NE FL and Camden county due to the potential for convergent bands setting up over areas that received 2-6+ inches in the past 24 hours. A few embedded thunderstorms could develop in the afternoon in north-central FL due to the proximity to the frontal boundary. Convection gradually tapers off late tonight with rounds of isolated to widely scattered showers shifting onshore to NE FL into early Thursday morning. Due to overcast skies and convection, daytime highs will be below seasonable in the upper 70s to low 80s. Overnight lows will range from the low 60s north to low 70s south.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/

Main Highlights This Period:

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

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

A wavy 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 gusty winds at the coast through the end of the week. Dry air will limit rain chances north of I-10 through Thursday before steering flow turns southerly through Friday which will allow the deeper moisture to gradually lift northward with developing warm front. Influence from what is likely to become Hurricane Isaias is expected Friday as gradients tighten between it 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' and 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.

Unknowns remain regarding soon-to-be Tropical Storm Isaias as it makes a turn to the north and pushes 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 TUESDAY/

Main Highlights This Period:

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

Strong southerly flow in response to the fast-moving tropical system 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.

Though there remains forecast uncertainty regarding Tropical Depression Nine's trajectory and speed across the Gulf, it does appear that the pseudo warm front evolving with the 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 perhaps tornadoes may be on the table 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. If forecast of TD9 shift the track farther east, these aforementioned threats will become a greater consideration.

Next week, a trailing cold front behind the remnant tropical low will push across the area bringing drier, sunnier, warmer and stable weather.

AVIATION /06Z WEDNESDAY THROUGH 06Z THURSDAY/

Local Nor'Easter remains intact with mainly IFR CIGS and MVFR CIGS in on/off rain showers. NE winds less than 10 kts prevail overnight and then increase after 15Z to sustained 10-15 kts and gusts around 20 kts. Highest winds will be for coastal TAF sites. Have TEMPO/PROB30s in for lower VSBYs when convergent bands shift onshore over a TAF site. Rain chances decrease for SSI with VCSH by 18Z.

MARINE

Small Craft Advisory conditions spread southward into the northeast Florida waters today. Prolonged onshore winds continue as weak low pressure off the east central Florida coast moves slowly eastward today and Thursday maintaining breezy northeasterly winds. Onshore winds may briefly decrease to Caution speeds on Thursday before strengthening back to Small Craft Advisory levels by late Friday as high pressure builds over the Mid-Atlantic states and wedges down the southeastern seaboard. The National Hurricane Center is monitoring Tropical Depression Nine 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 will surge south along the Georgia and northeast FL coast through today leading to strong rip currents and rough surf. High Risk for Rip Currents will likely continue through this weekend with continued breezy onshore flow.

FIRE WEATHER

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

A Flood Watch continues this morning as waves of convergent bands shift onshore bringing moderate to heavy rainfall to the Atlantic Coastal areas of Northeast Florida and Southeast Georgia. These areas have received 2-6+ inches in the past 24 hours. Additional rainfall amounts of 1 to 3 inches will be possible. The heavy rainfall may combine with higher than normal tidal levels and may worsen flood issues in some Atlantic Coastal and St. Johns River locations. The Watch covers the morning high tide cycle along the Atlantic Coast and into the St. Johns River Basin.

Portions of the St Marys, Satilla, Santa Fe and Alapaha Rivers have risen into flood stage in response to widespread 4 to 8 inch rainfall over the last several days. 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. However, portions of the Satilla and St Marys have reached Minor Flood stage but are generally beginning to peak. 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 82 63 81 66 / 10 0 0 10 SSI 80 71 82 73 / 40 10 20 30 JAX 81 71 82 70 / 70 30 30 50 SGJ 81 73 81 73 / 90 50 70 60 GNV 79 71 80 69 / 70 40 50 50 OCF 78 71 80 70 / 90 40 70 60

JAX WATCHES/WARNINGS/ADVISORIES

FL...Flood Watch until noon EDT today for FLZ024-038-124-125-132- 137-138-225-233-325-333-425-433-533-633. Coastal Flood Advisory until 5 AM 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 FLZ125-132- 137-225-325-633. GA...Flood Watch until noon EDT today for GAZ165-166. Coastal Flood Advisory until 5 AM 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- 470-472. Small Craft Advisory from 2 PM this afternoon to 2 AM EDT Thursday for AMZ454-474.