Tropical Storm Gordon Discussion Number 11
NWS National Hurricane Center Miami FL AL072018
1000 PM CDT Tue Sep 04 2018
Aircraft and radar imagery shows that the center of Gordon is
making landfall just west of the Alabama-Mississippi border. The
radar imagery has shown an increase in convection around the center
within the past couple of hours, and Doppler velocities have
increased to 65-75 kt at about 2500 feet. A NOAA Hurricane Hunter
aircraft has measured peak 700-mb flight-level winds of 63 kt.
These data support an initial intensity of 60 kt. A NOAA Coastal
Marine Observing site on Dauphin Island, Alabama has recently
reported sustained winds of 49 kt with a gust to 63 kt. Once the
center moves inland, Gordon should rapidly weaken and it is
forecast to become a tropical depression on Wednesday morning.
Gordon moved a little right of the previous forecast track this
evening, but the most recent aircraft fixes suggest the center has
jogged back toward the left. The longer-term motion estimate is
315/12 kt. A large deep-layer ridge located over the eastern
United States is forecast to steer Gordon northwestward at a slower
forward speed during the next couple of days. After that time, the
cyclone should turn northward, then northeastward around the
western periphery of the ridge. The updated NHC track is again
close to a blend of the various consensus aids, but is a little
right of previous forecast for the first 24-36 hours, primarily due
to the slightly more eastward initial position.
Key Messages:
1. Gordon is expected to bring life-threatening storm surge and
hurricane conditions to portions of the central Gulf Coast, where a
Storm Surge Warning and Hurricane Warning are in effect. The highest
storm surge is expected along the coasts of Mississippi and Alabama
from Biloxi to Dauphin Island tonight and early Wednesday. Tropical
storm conditions and storm surge will also affect portions of the
western Florida Panhandle.
2. Heavy rainfall from Gordon will affect the western Florida
Panhandle, southwest Alabama, southern and central Mississippi,
northeastern Louisiana, and southern Arkansas, where totals could
reach as high as 12 inches. This rainfall will cause flash flooding
in portions of these areas.
SUMMARY OF 700 PM CDT...0000 UTC...INFORMATION
----------------------------------------------
LOCATION...29.7N 87.9W
ABOUT 75 MI...125 KM SE OF BILOXI MISSISSIPPI
ABOUT 70 MI...115 KM S OF MOBILE ALABAMA
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES
Tropical Storm Gordon Discussion Number 8
NWS National Hurricane Center Miami FL AL072018
400 AM CDT Tue Sep 04 2018
Gordon has changed little in organization on geostationary
satellite images or on the WSR-88D radar presentation over the past
several hours. The storm has a small CDO with convective banding
features primarily over the eastern semicircle of the circulation.
Overall the cloud pattern is indicative of moderate westerly shear
over the system, likely associated with an upper-level trough near
the central Gulf of Mexico. An Air Force Reserve Unit Hurricane
Hunter aircraft investigated Gordon a few hours ago and reported
maximum SFMR-measured surface winds of 54 kt. On this basis the
intensity had been adjusted to 55 kt, which is somewhat above the
latest Dvorak estimates. It is assumed that the shear will not be
strong enough to inhibit at least some strengthening before
landfall, so the tropical cyclone is still forecast to become a
hurricane later today. The official forecast, prior to landfall, is
close to the latest LGEM intensity guidance, and near the upper end
of the guidance suite. Gordon should weaken rapidly after landfall
in the lower Mississippi Valley region.
The motion continues west-northwestward, or 300/15 kt. There is
little or no change to the NHC track prediction or forecast
reasoning from the previous advisory. Gordon is expected to move
along the southwestern periphery of a mid-level high pressure area
and make landfall along the north-central Gulf of Mexico coast
within 24 hours. After landfall, the cyclone is forecast to move
northwestward, along the western side of the high, at a reduced
forward speed. Late in the forecast period Gordon, or its
post-tropical remnant, should turn northward to north-northeastward
as it approaches the mid-latitude westerlies. The official track
forecast is near the model consensus and very close to the previous
NHC track.
Key Messages:
1. Gordon is expected to bring life-threatening storm surge and
hurricane conditions to portions of the central Gulf Coast where a
Storm Surge Warning and Hurricane Warning are in effect. Residents
in these areas should listen to advice from their local officials.
All preparations to protect life and property should be rushed to
completion, as tropical storm conditions are expected to arrive in
the warning areas this afternoon.
2. Heavy rainfall from Gordon will affect the western Florida
Panhandle, southern Alabama, southern Mississippi and Louisiana,
where totals could reach as high as 12 inches. This rainfall could
cause flash flooding.
Tropical Storm Gordon Special Discussion Number 4
NWS National Hurricane Center Miami FL AL072018
830 AM EDT Mon Sep 03 2018
Surface observations from the Florida Keys and southeast Florida,
along with Doppler velocity data from the Miami radar, indicate
that the disturbance has developed a closed surface circulation and
a well-defined center. Recent observations from a Weatherflow site
at Carys Fort Reef and radar data support increasing the maximum
winds to at least 40 kt. As a result of these data, the system has
been upgraded to Tropical Storm Gordon, the seventh named system of
the 2018 Atlantic hurricane season. An Air Force Reserve Unit
reconnaissance aircraft is enroute to investigate Gordon.
The initial motion estimate is 300/15 kt and the previous forecast
track remains unchanged. The intensity forecast was adjusted upward
in the first 24 to 36 hours to account for the initial increase in
intensity. Some additional adjustments may be required after the
reconnaissance aircraft completes its mission and provides more
detailed information on the stricture and intensity of Gordon.
Key Messages:
1. Gordon will bring heavy rainfall and tropical storm conditions to
portions of South Florida and the Florida Keys today and a Tropical
Storm Warning is in effect for these areas.
2. A Tropical Storm Warning is in effect for portions of the
central Gulf Coast, and tropical storm conditions are expected in
those areas beginning late Tuesday. Heavy rainfall from Gordon will
affect portions of the central Gulf Coast over the next few days,
including areas that have already received heavy rainfall from a
different weather system. Interests in these areas should monitor
products from their local National Weather Service office.
Potential Tropical Cyclone Seven Discussion Number 1
NWS National Hurricane Center Miami FL AL072018
500 PM EDT Sun Sep 02 2018
The area of disturbed weather associated with a tropical wave that
the NHC has been tracking for the past few days has become better
organized today. Strong winds previously associated with an upper-
level trough just west of the system have decreased significantly
during the day, and the upper-level flow across the disturbance has
become more anticyclonic. Earlier scatterometer wind data indicated
that the system does not yet have a closed surface circulation.
However, the same data indicate that winds of 25-28 kt exist outside
of thunderstorm activity, with some higher gusts likely present.
The initial intensity is being set at a conservative 25 kt for this
advisory.
The initial motion estimate is an uncertain 300/13 kt. The global
models are in excellent agreement that the strong subtropical ridge
to the north of the disturbance will remain entrenched across the
southeastern U.S. and mid-Atlantic states throughout the forecast
period. This flow pattern should keep the system moving in a west-
northwestward to northwestward motion until landfall occurs along
the central Gulf coast in 60-72 hours. The model tracks are tightly
packed, so the NHC official forecast track essentially lies down the
middle of the guidance envelope. On the forecast track, the system
is expected to move across the Florida Keys Monday afternoon, and
reach the central Gulf Coast by Tuesday night or Wednesday morning.
The aforementioned upper-level anticyclonic has been steadily
increasing during the day today, with weak cirrus outflow now
occurring in all quadrants. The disturbance is forecast to move
across the very warm waters of the Gulfstream late tonight and early
Monday morning where local diabatic heating should enhance deep
convection near the mid-level circulation, causing the vortex column
to build downward to the surface. Once a closed surface circulation
develops, the combination of low to modest vertical shear and SSTs
of at least 30C along the track should allow for at least slow but
steady strengthening. Although the official intensity forecast shows
weakening at 72 hours, this is due to the system expected to be
inland at that time. Conditions will favorable for continued
strengthening after the 48-h period until landfall occurs, and a
peak intensity of around 55 kt around 60 hours is possible. The
SHIPS and LGEM models were the only intensity guidance available for
this package, and the official forecast is just a little below an
average of those models. The HWRF and HMON models will be
forthcoming for the next advisory package, so some adjustments to
this first intensity forecast may be required as more guidance
becomes available.
Key Messages:
1. Potential Tropical Cyclone Seven will bring heavy rainfall and
gusty winds to portions of the Bahamas, South Florida, and the
Florida Keys tonight and Monday, and interests in those areas should
monitor the progress of this system.
2. A Tropical Storm Watch has been issued for portions of the
central Gulf Coast, and tropical storm conditions are possible in
those areas Tuesday night and Wednesday. Heavy rainfall from this
system will affect portions of the central Gulf Coast later this
week, including areas that are currently receiving heavy rainfall
from a different weather system. Interests in these areas should
monitor products from their local National Weather Service office.
3. Users should be aware that forecast uncertainty for potential
tropical cylones is generally larger than that for tropical
cyclones, especially beyond 48-72 hours.
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