BULLETIN
Tropical Storm Idalia Advisory Number 17
NWS National Hurricane Center Miami FL AL102023
500 PM EDT Wed Aug 30 2023
...IDALIA NOW A TROPICAL STORM...
...RISK OF FRESHWATER FLOODING, STORM SURGE, AND STRONG WINDS
CONTINUES ACROSS PORTIONS OF GEORGIA AND THE CAROLINAS...
SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...32.2N 81.7W
ABOUT 40 MI...65 KM W OF SAVANNAH GEORGIA
ABOUT 115 MI...180 KM WSW OF CHARLESTON SOUTH CAROLINA
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...NE OR 35 DEGREES AT 21 MPH...33 KM/H
MINIMUM CENTRAL PRESSURE...984 MB...29.06 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:
The Storm Surge Warnings and Watches have been discontinued along
the Gulf coast of Florida. The Storm Surge Watch has been
discontinued along the Georgia coast.
The Hurricane Warning along the coasts of Georgia and South
Carolina has been changed to a Tropical Storm Warning. The
Hurricane Watches have been discontinued.
The Tropical Storm Warnings have been discontinued along the Gulf
coast of Florida, and on the east coast of Florida south of the
Flagler/Volusia County Line.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT:
A Storm Surge Warning is in effect for...
* St. Catherine's Sound Georgia to South Santee River South Carolina
A Tropical Storm Warning is in effect for...
* Volusia/Brevard County Line Florida to the North Carolina/Virginia
border
* Pamlico and Albemarle Sounds
A Storm Surge Watch is in effect for...
* Beaufort Inlet to Ocracoke Inlet North Carolina
* Neuse and Pamlico Rivers North Carolina
A Storm Surge Warning means there is a danger of life-threatening
inundation, from rising water moving inland from the coastline in
the indicated locations. For a depiction of areas at risk, please
see the National Weather Service Storm Surge Watch/Warning Graphic,
available at hurricanes.gov. This is a life-threatening situation.
Persons located within these areas should take all necessary
actions to protect life and property from rising water and the
potential for other dangerous conditions. Promptly follow
evacuation and other instructions from local officials.
A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area.
A Storm Surge Watch means there is a possibility of life-
threatening inundation, from rising water moving inland from the
coastline in the indicated locations. For a depiction of areas at
risk, please see the National Weather Service Storm Surge
Watch/Warning Graphic, available at hurricanes.gov.
Interests in Bermuda should monitor the progress of Idalia.
For storm information specific to your area, including possible
inland watches and warnings, please monitor products issued by your
local National Weather Service forecast office.
DISCUSSION AND OUTLOOK
----------------------
At 500 PM EDT (2100 UTC), the center of Tropical Storm Idalia was
located over southeastern Georgia near latitude 32.2 North,
longitude 81.7 West. Idalia is moving toward the northeast near 21
mph (33 km/h), and this general motion is expected to continue
through tonight. A generally eastward motion is forecast to begin
on Thursday and continue through Saturday. On the forecast track,
the center of Idalia will move near or along the coasts of Georgia
and South Carolina through tonight, and then just offshore the
coast of North Carolina on Thursday. Idalia will then move
eastward over the western Atlantic into the weekend.
NOAA Doppler radar data indicate that maximum sustained winds have
decreased to near 70 mph (110 km/h) with higher gusts. Some
additional weakening is forecast through tonight, but Idalia is
expected to remain a tropical storm while it moves near the coasts
of Georgia, South Carolina, and North Carolina.
Tropical-storm-force winds extend outward up to 205 miles (335 km)
from the center. A sustained wind of 52 mph (83 km/h) and a gust
to 67 mph (107 km/h) were recently reported at the Savannah
Entrance Light.
The estimated minimum central pressure is 984 mb (29.06 inches).
HAZARDS AFFECTING LAND
----------------------
Key messages for Idalia can be found in the Tropical Cyclone
Discussion under AWIPS header MIATCDAT5 and WMO header WTNT45 KNHC,
and on the web at hurricanes.gov/text/MIATCDAT5.shtml
STORM SURGE: The combination of storm surge and tide will cause
normally dry areas near the coast to be flooded by rising waters
moving inland from the shoreline. The water could reach the
following heights above ground somewhere in the indicated areas if
the peak surge occurs at the time of high tide...
Savannah River to South Santee River, SC...3-5 ft
Saint Catherines Sound, GA to Savannah River...2-4 ft
Beaufort Inlet, NC to Ocracoke Inlet, NC...2-4 ft
Neuse and Bay Rivers...2-4 ft
Pamlico and Pungo Rivers...2-4 ft
South Santee River, SC to Beaufort Inlet, NC...1-3 ft
Ochlockonee River, FL to East Cape Sable, FL...1-3 ft
Tampa Bay...1-3 ft
Charlotte Harbor...1-3 ft
Flagler/Volusia County Line, FL to Saint Catherines Sound, GA...1-3
ft
Ocracoke Inlet, NC to Duck, NC...1-3 ft
The deepest water will occur along the immediate coast in areas of
onshore winds, where the surge will be accompanied by large waves.
Surge-related flooding depends on the relative timing of the surge
and the tidal cycle, and can vary greatly over short distances. For
information specific to your area, please see products issued by
your local National Weather Service forecast office.
WIND: Tropical storm conditions are occurring within the tropical
storm warning area along the northeastern coast of Florida,
Georgia, and South Carolina, and will spread across coastal
sections of North Carolina tonight through Thursday.
RAINFALL: Idalia is expected to produce a swath of 4 to 8 inches of
rainfall with isolated maxima up to 10 inches from east-central
Georgia through central to eastern South Carolina and eastern North
Carolina into Thursday. These rainfall amounts will lead to areas
of flash, urban, and moderate river flooding, with considerable
impacts. The trailing moisture band from Idalia has the potential
to produce additional rainfall amounts of 1 to 2 inches across the
west coast of Florida.
SURF: Swells generated by Idalia along the eastern and central Gulf
coast will subside tonight and Thursday. Swells will affect the
southeastern U.S. coast during the next few days. These swells are
likely to cause life-threatening surf and rip current conditions.
Please consult products from your local weather office.
TORNADOES: A few tornadoes will be possible through this evening
across coastal South Carolina and through tonight across southern
coastal North Carolina.
NEXT ADVISORY
-------------
Next intermediate advisory at 800 PM EDT.
Next complete advisory at 1100 PM EDT.
$$
Forecaster Berg
Tropical Storm Idalia Discussion Number 17
NWS National Hurricane Center Miami FL AL102023
500 PM EDT Wed Aug 30 2023
Idalia's radar and satellite presentation has become increasingly
asymmetric. A coastal front appears to have developed just inland
of the coasts of Georgia and South Carolina, with heavy rainfall
being enhanced along and to the northwest of this boundary. The
highest WSR-88D velocities observed are about 60-65 kt at an
elevation of 5000 feet, indicating that Idalia is no longer a
hurricane. The advisory intensity is set at 60 kt, which is
probably a bit generous.
The initial motion is now northeastward, or 035/18 kt, with Idalia
moving between the northwestern periphery of a mid-level ridge
located over the Greater Antilles and a deep-layer trough moving
across the northeastern U.S. The storm is expected to turn toward
the east and east-southeast during the next 48 hours, but then slow
down considerably as the trough lifts out and leaves Idalia behind.
There is fairly high confidence that Idalia will move slowly
eastward over the western Atlantic, in the vicinity of Bermuda,
during the latter part of the forecast period, although there is
less confidence in the details of that motion due to large model
spread.
Additional weakening is expected while Idalia's center continues
moving over land through tonight. However, once the center moves
back offshore on Thursday, model fields suggest that Idalia could
interact with the aforementioned coastal front, with an area of
stronger winds developing along the boundary near eastern North
Carolina during the day. Based on this scenario, the NHC intensity
forecast closely follows the GFS solution at 24 and 36 hours.
After 36 hours, there is more uncertainty on Idalia's intensity and
structure. Some guidance suggests that Idalia will continue
interacting with the front and possibly become post-tropical,
particularly if it struggles to maintain organized deep convection.
For now, the NHC forecast keeps Idalia as a tropical storm for the
entire forecast period.
KEY MESSAGES:
1. Storm surge is expected along the southeastern U.S. coast within
the Storm Surge Warning area through tonight. Coastal flooding is
also expected within the Storm Surge Watch area in North Carolina on
Thursday. Residents in these areas should follow any advice given
by local officials.
2. Tropical-storm-force winds will affect portions of the
southeastern U.S. coast through Thursday.
3. Areas of flash, urban, and moderate river flooding, with
considerable impacts, are expected from east central Georgia,
through eastern South Carolina and eastern North Carolina into
Thursday.
FORECAST POSITIONS AND MAX WINDS
INIT 30/2100Z 32.2N 81.7W 60 KT 70 MPH...INLAND
12H 31/0600Z 33.4N 79.3W 50 KT 60 MPH...INLAND
24H 31/1800Z 34.1N 75.7W 50 KT 60 MPH...OVER WATER
36H 01/0600Z 33.7N 72.2W 45 KT 50 MPH
48H 01/1800Z 32.8N 69.7W 45 KT 50 MPH
60H 02/0600Z 32.1N 68.2W 45 KT 50 MPH
72H 02/1800Z 31.7N 67.3W 45 KT 50 MPH
96H 03/1800Z 32.3N 65.1W 45 KT 50 MPH
120H 04/1800Z 34.4N 61.3W 45 KT 50 MPH
$$
Forecaster Berg
