Marine Weather Net

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


TONIGHT

SW
WINDS
10
KNOTS

WEDNESDAY

W
WINDS
5 - 10
KNOTS

WEDNESDAY NIGHT

W
WINDS
5 - 10
KNOTS

THURSDAY

NW
WINDS
5 KNOTS

The Marine Weather Forecast In Detail:
AMZ454 Forecast Issued: 850 PM EDT Tue Jul 27 2021

Tonight...Southwest Winds 10 Knots Becoming West 5 To 10 Knots After Midnight. Seas 3 To 4 Feet With A Dominant Period 9 Seconds. Mostly Smooth On The Intracoastal Waters. Chance Of Showers And Thunderstorms In The Evening, Then Slight Chance Of Showers And Thunderstorms After Midnight.
Wednesday...West Winds 5 To 10 Knots Becoming Southeast 5 Knots In The Afternoon. Seas 2 To 3 Feet With A Dominant Period 9 Seconds. A Light Chop On The Intracoastal Waters. Chance Of Showers And Thunderstorms.
Wednesday Night...West Winds 5 To 10 Knots. Seas 2 To 3 Feet With A Dominant Period 8 Seconds. Mostly Smooth On The Intracoastal Waters. Chance Of Showers And Thunderstorms In The Evening, Then Slight Chance Of Showers And Thunderstorms After Midnight.
Thursday...Northwest Winds 5 Knots Becoming East 5 To 10 Knots In The Afternoon. Seas 2 To 3 Feet. A Light Chop On The Intracoastal Waters. Slight Chance Of Showers And Thunderstorms In The Morning, Then Chance Of Showers And Thunderstorms In The Afternoon.
Thursday Night...South Winds 10 To 15 Knots Becoming Southwest 5 To 10 Knots After Midnight. Seas 2 To 3 Feet. A Light Chop On The Intracoastal Waters. Slight Chance Of Showers And Thunderstorms In The Evening.
Friday...South Winds 5 To 10 Knots. Seas 2 To 3 Feet. A Light Chop On The Intracoastal Waters. Slight Chance Of Showers And Thunderstorms.
Friday Night...Southwest Winds 10 To 15 Knots. Seas 2 To 3 Feet.
Saturday...Southwest Winds 5 To 10 Knots. Seas 2 To 3 Feet. Chance Of Showers And Thunderstorms.
Saturday Night...Southwest Winds 10 To 15 Knots. Seas 2 To 3 Feet. Slight Chance Of Showers And Thunderstorms.
Sunday...Southwest Winds 10 To 15 Knots. Seas 2 To 3 Feet. Chance Of Showers And Thunderstorms.
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AMZ400: Synopsis for Altamaha Sound GA to Flagler Beach FL out to 60 nm
850 PM EDT Tue Jul 27 2021

A weak area of low pressure near the Georgia and South Carolina border will move across the coastal waters through Wednesday. Numerous thunderstorms developing over land on Wednesday afternoon will move across our local waters during the late afternoon and evening hours, with stronger activity containing frequent lightning strikes and briefly gusty winds. A couple of surface troughs will edge southward across the local waters through the week bringing increased daily rain chances with high pressure remaining south of the region.

Gulf Stream
The approximate location of the west wall of the Gulf Stream as of Jul 27, 2021 at 1200 UTC...
- 56 nautical miles east northeast of Flagler Beach.
- 57 nautical miles east of Saint Augustine Beach.
- 61 nautical miles east of Jacksonville Beach.
- 67 nautical miles east of St Simons Island.
Area Forecast Discussion
National Weather Service Jacksonville FL
911pm EDT Tuesday July 27 2021

Forecast remains on track. Best chance for rain overnight remains over southeast Georgia with storms popping up along outflow boundaries. Storms will be slow-movers with heavy rain, localized flooding and frequent lightning as the main hazards. With the loss of diurnal heating, storms will slowly diminish overnight. Lows tonight will be in the mid 70s.

.NEAR TERM [Through Wednesday]... Focus for convective development through the late evening hours will shift to southeast GA, where plenty of surface based CAPE remains per latest LAPS/RAP analyses, especially along the inland corridor from Waycross to Jesup. Stronger convection this evening will be capable of producing localized flooding due to slow storm motion, along with frequent lightning strikes and briefly gusty winds. Latest short-term, high resolution guidance indicates that mesoscale boundary collisions could keep convection firing through around or just after midnight, while activity mostly winds down across northeast and north central FL, where debris cloud cover should thin out during the late evening hours, while mid and high altitude cloudiness could linger through the predawn hours across southeast GA. Lows will mostly fall to the mid 70s.

A shortwave trough will dive into the southeastern states on Wednesday afternoon, which will result in another active afternoon and evening of convection as the weak surface trough tied to Invest 90L progresses slowly southward across the Altamaha River. Deep tropical moisture will remain in place to the south of this trough, and we expect convection to initially be triggered by the inland moving Gulf coast sea breeze by the late morning hours in western portions of the Suwannee Valley. Mesoscale boundary collisions will then increase coverage and intensity of convection by late afternoon as activity generally moves slowly eastward, with a few storms possibly pulsing towards late afternoon as convection encounters the pinned Atlantic sea breeze boundary at coastal locations. Localized flooding will be possible due to slow storm motion, particularly at urban and normally flood prone locations. Storms that pulse will produce frequent lightning strikes and briefly gusty downburst winds up to 40 mph. Highs will climb to the upper 80s to near 90 before convection and cloud cover increase during the early to mid afternoon hours, with maximum heat index values around 100.

.SHORT TERM [Wednesday Night Through Friday Night]... A massive "heat dome" ridge currently centered over the Rockies will nose into the southeastern states late this week as shortwave troughing departs our region. Low level troughing will be slow to depart northeast and north central FL on Thursday. Scattered to numerous afternoon and early evening thunderstorms will be focused to the south of Interstate 10, with mesoscale boundary collisions possibly developing widely scattered convection over southeast GA. Rising heigheights aloft and less convective coverage over southeast GA will allow highs to soar to the mid and upper 90s inland, with an earlier developing Atlantic sea breeze boundary keeping coastal highs closer to 90. Highs elsewhere will likely reach the lower 90s before convective coverage increases. The bigger story will be soaring heat index values, with maximum values reaching the 105-110 range for locations along and north of I-10 and 100-105 for locations south of I-10. Convection will mostly dissipate before midnight on Wednesday and Thursday evenings, with lows generally in the mid 70s inland and the upper 70s at coastal locations.

Low level troughing will shift over central FL on Friday, with PWAT (Precipitable Water) values falling to around 1.75 inches and subsidence aloft strengthening as the heat dome becomes centered over the Southern Plains states and extends its axis southeastward over the Deep South. Dry weather is expected across most of southeast GA, while only widely scattered convection develops during the late afternoon and early evening hours across northeast and north central FL. Highs will soar to the upper 90s across most of inland southeast GA, with mid to upper 90s elsewhere at inland locations and low to mid 90s all the way to area beaches. Heat index values should reach Heat Advisory criteria, with most areas experiencing maximum values of 108-112 degrees by the afternoon hours. Lows Friday night will only fall to the mid to upper 70s inland and around 80 at coastal locations.

.LONG TERM [Friday Night Through Monday Night]... Troughing diving southeastward across the Great Lakes region this weekend will gradually suppress the heat dome ridge and will drive a cold front into the Deep South by Sunday. Heat index values on Saturday will likely reach Heat Advisory criteria once again, but thunderstorm coverage will begin to increase by the late afternoon and early evening hours as PWAT (Precipitable Water) values begin to climb back towards 2 inches across our region to the south of the approaching frontal boundary. Inland highs on Saturday will reach the mid to upper 90s, with low to mid 90s all the way to area beaches. Thunderstorm coverage will then become widespread by Sunday afternoons the front edges closet to our area. Deep west southwesterly flow will still bring highs up to the low and mid 90s before convection becomes widespread during the mid to late afternoon hours. Heat index values on Sunday will flirt with Heat Advisory criteria, with values generally in the 105-110 range before cloud cover and convection increases later in the afternoon. We expect widespread thunderstorms to occur on Monday afternoon as the front settles over southeast GA, and highs will fall back to the upper 80s to lower 90s. Lows will continue to only fall to the mid and upper 70s this weekend and early next week, except around 80 at coastal locations.

NOAA Jacksonville FL Office: Watches - Warnings - Advisories
FL...None. GA...None. AM...None.