[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 051250 AAA
TWDAT

Tropical Weather Discussion...UPDATED
NWS National Hurricane Center Miami FL
805 AM EDT Wed Sep 5 2018

UPDATED FOR T.D. GORDON AND HURRICANE FLORENCE INFORMATION

Tropical Weather Discussion for North America, Central America
Gulf of Mexico, Caribbean Sea, northern sections of South
America, and Atlantic Ocean to the African coast from the
Equator to 32N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 0600 UTC surface analysis and satellite imagery through
1230 UTC.

...SPECIAL FEATURES...

Tropical Storm GORDON has weakened to a Tropical Depression,
after making landfall, and moving inland more and more. The
center of Tropical Depression GORDON, at 05/1200 UTC, is in
central Mississippi, near 32.0N 89.9W, or 22 nm/40 km to the SSE
of Jackson in Mississippi. GORDON is moving NW, or 325 degrees,
12 knots. The estimated minimum central pressure is 1002 mb. The
maximum sustained wind speeds are 30 knots with gusts to 40
knots.
The threat continues for heavy rain and flooding. Scattered
moderate to isolated strong rainshowers cover the U.S.A. and the
waters of the Gulf of Mexico from 28N northward, across the
Florida Panhandle to northern Alabama between 84W and western
Georgia and 91W in western Mississippi. Public Advisories for
GORDON are issued under the WMO/AWIPS headers WTNT32
KNHC/MIATCPAT2. Forecast advisories for GORDON are issued under
WMO/AWIPS headers WTNT22 KNHC/MIATCMAT2.

The center of Hurricane FLORENCE, at 05/0900 UTC, is near 21.4N
44.8W. FLORENCE is moving NW, or 305 degrees, 11 knots. The
estimated minimum central pressure is 976 mb. The maximum
sustained wind speeds are 90 knots with gusts to 110 knots.
Scattered to numerous strong rainshowers are within 90 nm of the
center in the W semicircle, and within 60 nm of the center in the
E semicircle. Scattered moderate to isolated strong rainshowers
are elsewhere within 120 nm of the center in all directions.
Isolated moderate rainshowers are in the remainder of the area
from 20N to 24N between 42W and 49W. Public Advisories for
FLORENCE are issued under WMO/AWIPS headers WTNT31 KNHC/
MIATCPAT1. Forecast Advisories for FLORENCE are issued under
WMO/AWIPS headers WTNT21 KNHC/MIATCMAT1.

A tropical wave is along 26W/27W from 20N southward. A 1007 mb
low pressure center is along the wave near 11N. Environmental
conditions are forecast to be conducive for additional
development. A tropical depression is expected to form by the
end of the week, as the system moves WNW, across the tropical
Atlantic Ocean. Widely scattered moderate to isolated strong
rainshowers are within 90 nm on either side of the line that
runs from 07N33W to 12N29W to 16N26W. This system has a medium
chance of becoming a tropical cyclone during the next 48 hours.
Please read the latest NHC Tropical Weather Outlook under
AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more information.

...TROPICAL WAVES...

A Caribbean Sea tropical wave is along 80W/81W from Cuba
southward. The wave is moving through the area of an upper level
NE-to-SW oriented cyclonic shear axis. Isolated moderate to
locally strong rainshowers are in the NW corner of the Caribbean
SEA.

A tropical wave is along 97W/98W from 21N southward into the
eastern Pacific Ocean. The tropical wave just has moved through
the SW corner of the Gulf of Mexico.

...MONSOON TROUGH/ITCZ...

The monsoon trough passes through the coastal sections of Senegal
near 16N17W, to the 1007 mb low pressure center that is part of
the SPECIAL FEATURES section with the 26W/27W tropical wave, to
08N32W, to 08N36W. The ITCZ is along 09N48W 06N57W. Widely
scattered moderate to isolated strong rainshowers are from 05N to
12N between land and 21W. Isolated moderate rainshowers are from
05N to 10N between 40W and 60W, and from 05N southward between
27W and 44W.

...DISCUSSION...

GULF OF MEXICO...

Please read the SPECIAL FEATURES section for details about
Tropical Storm Gordon.

An upper-level inverted trough is to the west of Gordon, from
southeastern Louisiana to an upper-level cyclonic circulation
just northwest of the Yucatan Peninsula near 22N91W and to the
eastern Bay of Campeche. An upper-level ridge extends from
southwestern Louisiana to inland northeastern Mexico.
Aside from convection associated with Tropical Storm Gordon,
the availability of ample moisture along with the presence of
the upper trough and low is allowing for the atmosphere to be
unstable over much of the western and central gulf waters. As a
result, scattered showers and isolated thunderstorms are seen
west of 90W, with the most of the activity mainly occurring to
the west of 94W. Isolated showers and thunderstorms are
elsewhere over the remainder of the gulf. The shower and
thunderstorm activity should remain quite active through this
evening.

Tropical Storm Gordon is now inland over southeast Mississippi.
Winds and seas over the northern Gulf between Apalachicola and
the mouth of the Mississippi River will be subsiding through
early morning. Weak ridging will build from the Carolinas to the
coast of Texas in the wake of Gordon, supporting gentle to
moderate easterly winds and modest seas into early next week. The
exception will be fresh winds pulsing off the west of coast of
the Yucatan peninsula, mainly during the late evening, due to a
daily trough that sets up over the southwest Gulf.

CARIBBEAN SEA...

An upper-level cyclonic shear axis is noted on water vapor
imagery extending in NE to SW fashion from an elongated cyclonic
circulation well north of the Caribbean southwestward to central
Hispaniola, to near 15N76W and to central Panama. This feature is
interacting with the tropical wave along 77W/78W initiating deep
convection just south of central Cuba as described above under
the Tropical Waves section. Otherwise, isolated showers and
thunderstorms are over the remainder of the Caribbean west of
79W, while isolated showers are east of 79W.

The easternmost sector of the eastern Pacific monsoon stretches
along 09N/10N to across northern Panama, to the far SW Caribbean,
and to northwestern Colombia. Widely scattered showers and
isolated thunderstorms are seen from 09N-10N east of 81W to
inland northwestern Colombia.

The tropical wave along 77W/78W will move across the rest of the
central Caribbean through this morning, then across the western
Caribbean later on Wed and through Fri. The gradient associated
with a relatively weak surface ridge, that is to the north of the
region, will maintain moderate to fresh trade winds mostly
everywhere, through the next several days.

A relatively weak surface ridge in the western Atlantic Ocean
will maintain moderate to fresh trade winds in most of the region
through late Sunday.

ATLANTIC OCEAN...

Please read the SPECIAL FEATURES section for details about
Hurricane Florence. A second area of interest pertains to a
new area of broad low pressure, in the far eastern Atlantic
Ocean, with a medium chance of tropical cyclone formation during
the next 48 hours.

An elongated upper-level cyclonic circulation is near 26N66W,
with a trough extending southwestward to Hispaniola. Upper-level
cyclonic wind flow covers the area north of 19N between 57W and
77W. At the surface, a trough is analyzed from near 21N63W to
31N60W. Scattered showers and thunderstorms are noted north of
22N between 61W and 70W. Isolated showers and weak isolated
thunderstorms are elsewhere west of 59W.

Strong high pressure to the north and northeast of Hurricane
Florence is suppressing the atmosphere environment, maintaining
it pretty stable over the eastern Atlantic, except near the broad
area of low pressure as described above.

A weak pressure pattern will maintain gentle to moderate easterly
winds across the area through Sunday night. Easterly swell from
Hurricane Florence will move into the open waters that are to
the east of the Bahamas, from late tonight through Sunday.

For additional information please visit
http://www.hurricanes.gov/marine

$$
ja/mt
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