Marine Weather Net

Fernandina Beach to St. Augustine, FL Out 20 NM Marine Forecast


TONIGHT

S
WINDS
15 - 20
KNOTS

THURSDAY

SW
WINDS
10 - 15
KNOTS

THURSDAY NIGHT

W
WINDS
10 - 15
KNOTS

FRIDAY

N
WINDS
5 - 10
KNOTS

The Marine Weather Forecast In Detail:
AMZ452 Forecast Issued: 326 PM EDT Wed Apr 14 2021

SMALL CRAFT ADVISORY IN EFFECT UNTIL 11 PM EDT THIS EVENING
Tonight...South Winds 15 To 20 Knots With Frequent Gusts Up To 30 Knots. Seas 4 To 6 Feet With A Dominant Period 9 Seconds. Choppy On The Intracoastal Waters.
Thursday...Southwest Winds 10 To 15 Knots. Seas 4 To 6 Feet With A Dominant Period 9 Seconds. A Moderate Chop On The Intracoastal Waters. Slight Chance Of Showers In The Morning, Then Chance Of Showers And Slight Chance Of Thunderstorms In The Afternoon.
Thursday Night...West Winds 10 To 15 Knots Becoming Northwest After Midnight. Seas 3 To 5 Feet With A Dominant Period 9 Seconds. A Light Chop On The Intracoastal Waters. Chance Of Showers And Slight Chance Of Thunderstorms In The Evening, Then Slight Chance Of Showers After Midnight.
Friday...North Winds 5 To 10 Knots. Seas 3 To 4 Feet. A Light Chop On The Intracoastal Waters. Slight Chance Of Showers.
Friday Night...East Winds 5 To 10 Knots Becoming Southeast 5 Knots After Midnight. Seas 2 To 3 Feet. Mostly Smooth On The Intracoastal Waters. Slight Chance Of Showers After Midnight.
Saturday...South Winds 10 To 15 Knots. Seas 3 To 4 Feet. A Moderate Chop On The Intracoastal Waters. Chance Of Showers.
Saturday Night...Southwest Winds 10 To 15 Knots Becoming West 5 To 10 Knots After Midnight. Seas 3 To 4 Feet. Chance Of Showers And Thunderstorms.
Sunday...Northwest Winds 5 To 10 Knots. Seas 3 To 4 Feet. Showers Likely And Chance Of Thunderstorms.
Sunday Night...West Winds 5 To 10 Knots. Seas 2 To 3 Feet. Showers Likely And Chance Of Thunderstorms.
Monday...North Winds 5 To 10 Knots Becoming Northeast In The Afternoon. Seas 2 To 3 Feet. Chance Of Showers And Slight Chance Of Thunderstorms.
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AMZ400: Synopsis for Altamaha Sound GA to Flagler Beach FL out to 60 nm
326 PM EDT Wed Apr 14 2021

Tightened pressure gradient will lead to hazardous wind gusts this evening. Caution-level winds (15-20 knots) will continue into Thursday as they veer southwesterly ahead of an approaching cold front. Front will bring shower and storm chances over area waters late tomorrow afternoon and through the evening. Winds will subside and veer northerly behind the front on Friday. A series of weather disturbances and associated fronts will lead to a period of unsettled weather this weekend and through early next week.

Gulf Stream
The approximate location of the west wall of the Gulf Stream as of Apr 13, 2021 at 1200 UTC...
- 58 nautical miles east northeast of Flagler Beach.
- 65 nautical miles east of Saint Augustine Beach.
- 77 nautical miles east southeast of Jacksonville Beach.
- 99 nautical miles east southeast of St Simons Island.
Area Forecast Discussion
National Weather Service Jacksonville FL
950pm EDT Wednesday April 14 2021

...FEW STRONG THUNDERSTORMS POSSIBLE ON THURSDAY AFTERNOON WEST OF U.S. HIGHWAY 301... Late evening surface analysis depicts a cold front stretching from the southern Appalachians southwestward across the Tennessee and lower Mississippi Valleys. Meanwhile, high pressure (1020 millibars) was weakening as it shifts southeastward off the southeastern seaboard. Aloft...a slow moving cutoff trough was positioned over the Great Lakes region, creating fast zonal flow aloft across the southern tier of the nation. Shortwave energy embedded within this zonal flow pattern was traversing the Deep South and the Southern Plains states. Shortwave energy entering our region had just enough moisture and convergence, compliments of colliding sea breezes along the U.S. Highway 301 corridor, to develop a batch of briefly intense showers earlier this evening. This activity has since moved offshore of coastal southeast GA, while another area of showers was weakening as it moves across Interstate 75 in far southern GA. Mid and high altitude cloud cover was thinning as it advects over our region. Temperatures at 01Z were still mostly in the 70s across our area, with dewpoints ranging from the upper 40s near the Altamaha and Ocmulgee Rivers to the mid and upper 60s at coastal locations, where breezy southerly winds prevail as our local pressure gradient tightens due to high pressure moving offshore and the frontal boundary approaching from the west.

Shortwave energy will weaken over the southeastern states as it moves southeastward overnight, bringing shower coverage to a close. However, abundant mid and high altitude cloudiness and a tight pressure gradient will limit fog and low stratus development as our lower troposphere only slowly moistens, and lows will only fall to the 60-65 degree range, which is about 5-10 degrees above mid-April climatology.

The cutoff trough over the Great Lakes region will only gradually shift southeastward on Thursday, nudging a weak cold front through our region during the afternoon and evening hours. An upstream batch of shortwave energy that is currently igniting convection along the Upper Texas coast will also enter our area during the afternoon hours, which will trigger a line of showers and embedded thunderstorms over the FL panhandle and southwestern GA towards daybreak. The northwestern edge of this convective line should enter our inland southeast GA counties and the far western Suwannee Valley during the late morning hours on Thursday. Thickening cloud cover will likely limit surface-based instability, but steepening lapse rates ahead of the upstream shortwave may trigger a strong storm or two, mainly for our inland southeast GA and Suwannee Valley locations during the early to mid afternoon hours. The main threats with any stronger storms in these areas will be strong wind gusts of 40-50 mph and small hail. Instability will remain limited for locations east of U.S. Highway 301, with just isolated thunderstorms expected along the I-95 corridor during the mid to late afternoon hours. Cloud cover and convection arriving during the late morning hours will keep highs in the 70s across southeast GA and the far western Suwannee Valley, while highs along and east of U.S. Highway 301 in northeast and north central FL will climb to the low to mid 80s before rain chances increase by mid-afternoon. A tight local pressure gradient ahead of the front will generate breezy west- southwesterly winds for locations where rainfall holds off until later in the day.

Marine
A cold front entering the southeastern states this evening will push southeastward overnight and Thursday, crossing the Georgia waters during the afternoon and the northeast Florida waters on Thursday evening. A surge of southerly winds ahead of this front this evening will produce Caution conditions near shore and Small Craft Advisory conditions offshore through the predawn hours on Thursday. Seas near shore of 4-6 feet will begin to subside towards sunrise, while seas offshore of 5-7 feet will prevail through the predawn hours. Caution level winds and seas will prevail through at least early afternoon on Thursday for the offshore waters.

The cold front will then stall over central Florida on Friday night as low pressure develops over the lower Mississippi Valley and moves eastward. This low pressure center will cross southern Georgia on Saturday and will move offshore on Saturday night, with a weak frontal boundary then lingering over the northeast Florida waters through the middle portion of next week. Waves of showers and thunderstorms will impact our waters from this weekend through Wednesday.

Rip Currents
A persistent long period northeasterly ocean swell will keep a moderate rip current risk in place at the northeast FL beaches on Thursday. A low risk is anticipated for the southeast GA beaches.

Fire Weather
Strong southwesterly transport winds will develop for locations from Waycross southward by the mid-morning hours on Thursday. Breezy west-southwesterly surface winds are expected across coastal portions of southeast GA and throughout northeast and north central FL by the late morning hours, with marginally high dispersion values possible east of Interstate 75 until rainfall arrives during the mid to late afternoon hours. A few strong thunderstorms will be possible over inland portions of southeast GA and in the Suwannee Valley through mid-afternoon, with briefly strong wind gusts and small hail being the primary threats.

Near Term - Through Tonight
A surface trough axis to the north has extended southward into SE GA/NE FL this afternoon. With a surface ridge situated to the east (north of Grand Bahama) of that trough axis (north of Grand Bahama), the gradient has tightened allowing a stronger Atlantic sea breeze. Gusts as strong as 25 mph are possible along the immediate coast through the early evening. A Gulf/Atlantic sea breeze merger around 7 or 8 pm this evening may generate a brief shower or two between Highway 301 and the I-95 corridor. Any showers that develop will be steered eastward into the Atlantic.

Westerly flow aloft will direct a mid-level impulse and considerable cloud cover overhead tonight. The associated showers will be limited by dry low levels and result in virga or very light rainfall, producing a few hundreths at most. Cloudiness overnight will limit cooling with low temperature readings in the low to mid 60s.

Short Term - Thursday Through Friday Night
Thursday will be an active day as a slow-moving cold front edges toward the area from the northeast. Pre-frontal troughing and associated convection will slowly push southeastward Thursday, reaching the I-10 corridor by the mid afternoon. Gusty pre-frontal winds are expected ahead of the pre-frontal activity, with gusts up to 30 mph.

There is some uncertainty in the potential for strong to severe storms as instability may be hampered by cloud cover and weaker mid- level lapse rates. Sufficient moisture advection into the Suwannee Valley may allow storms to overcome those stabilizing factors. That said, best chances form strong storms will be across the Suwannee Valley where instability will likely be maximized amid increasing kinematics (SRH). Further east, chances for showers and and run- of- the- mill t-storms are still expected along the front as it presses southward toward central FL during the afternoon and evening. Most of the area will dry out Thursday night, with the exception of the southern Zones where scattered showers may continue along the stalling front. The area will be between shortwave troughs on Friday which will translate to rain- free but cloudy conditions.

Considerable variability in high temps on Thursday as the front pushes across the area. Locations across NE FL and coastal SE GA are forecast to trend above normal amid southerly flow with highs in the mid to upper 80s. More cloud cover and early convection across inland SE GA will limit highs to the mid 70s. Cooler conditions are expected on Friday with near normal highs areawide.

Long Term - Saturday Through Wednesday
A prolonged period of unsettled weather carrying the potential for heavy rainfall is expected this weekend and into early next week as a series of mid-level waves and fronts influence the local weather.

The first shortwave will lift a stalled front across central FL northward as a warm front on Saturday. The heaviest rainfall is expected along and just north of that warm front as it lifts, with the heaviest rainfall likely across portions of southeast GA where an inch or two of rain cannot be ruled out. Then a trailing cold front will bring a second chance of showers and storms to the area on Sunday as it presses into central Florida and eventually stalling there on Monday. Similar to the evolution over the weekend, that front is forecast to drift northward on Tuesday, renewing rain/storm chances. There is some light at the end of this gloomy forecast tunnel, as a sweeping front is forecast to, at least temporarily, shunt the unsettled weather well to our south and east on Wednesday.

Confidence in the temperature forecast is fairly low as convection and vicinity frontal zones will greatly influence readings. Current forecast does favor highs in the mid to upper 70s and lows in the upper 50s to low 60s.

NOAA Jacksonville FL Office: Watches - Warnings - Advisories
FL...None. GA...None. AM...Small Craft Advisory until 5am EDT Thursday for Waters from Altamaha Sound GA to Fernandina Beach FL from 20 to 60 NM- Waters from Fernandina Beach to St. Augustine FL from 20 to 60 NM-Waters from St. Augustine to Flagler Beach FL from 20 to 60 NM..