[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 131202
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
802 AM EDT Thu Sep 13 2018

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
1130 UTC.

...SPECIAL FEATURES...

The center of Hurricane Florence at 13/1200 UTC is near 33.1N
75.1W. FLORENCE is moving NW, or 315 degrees, 10 knots. This
position is about 275 km ESE of Wilmington in North Carolina, and
about 355 km E of Myrtle Beach in South Caroling. The estimated
minimum central pressure is 956 mb. The maximum sustained wind
speeds are 95 knots with gusts to 115 knots. Scattered moderate to
strong convection is from 30N- 35N between 69W-76W. The present
NW motion is forecast to continue through Thu with a gradual
decrease in forward speed. A turn to the west- northwest and west
at an even slower forward speed is expected Thursday night and
Friday, and a slow west- southwestward motion is forecast Friday
night and Saturday. On the forecast track, the center of Florence
will approach the coasts of North and South Carolina on Thursday,
then move near or over the coast of southern North Carolina and
eastern South Carolina in the hurricane warning area on Thursday
night and Friday. A slow motion over eastern South Carolina is
forecast Friday night and Saturday. Florence is a high end
category 2 hurricane on the Saffir-Simpson Hurricane Wind Scale.
Little change in strength is expected before the center reaches
the coast, with weakening expected after the center moves inland.
Public Advisories for Florence are issued under WMO header WTNT31
KNHC and under AWIPS header MIATCPAT1. Forecast/ Advisories for
Florence are issued under WMO header WTNT21 KNHC and under AWIPS
header MIATCMAT1.

Tropical Storm Isaac centered near 15.4N 59.7W at 13/0900 UTC or
190 nm E of Dominica moving W 15 kt. The estimated minimum
central pressure is 1006 mb. The maximum sustained wind speeds are
40 knots with gusts to 50 knots. Scattered moderate convection is
from 13N- 17N between 54W-58W. A westward motion with a decrease
in forward speed is expected to continue through the weekend. On
the forecast track, Isaac is forecast to move across the central
Lesser Antilles and into the eastern Caribbean Sea on Thursday,
and then move across the eastern and central Caribbean Sea through
the weekend. Public Advisories for Isaac are issued under WMO
header WTNT34 KNHC and under AWIPS header MIATCPAT4. Forecast/
Advisories for Isaac are issued under WMO header WTNT24 KNHC and
under AWIPS header MIATCMAT4.

Hurricane Helene centered near 23.5N 37.3W at 13/0900 UTC or 1100
nm SSW of Lajes Air Base In The Azores moving N at 12 kt.
The estimated minimum central pressure is 986 mb. The maximum
sustained wind speeds are 65 knots with gusts to 80 knots.
Scattered moderate to strong convection is from 22N-27N between
34W-39W. A turn toward the north-northeast with an increase in
forward speed is expected Thursday night followed by a turn toward
the northeast over the weekend. Continued weakening is forecast
over the next couple of days, and Helene is expected to become a
tropical storm on Thursday. Public Advisories for Helene are
issued under WMO header WTNT33 KNHC and under AWIPS header
MIATCPAT3. Forecast/ Advisories for Helene are issued under WMO
header WTNT23 KNHC and under AWIPS header MIATCMAT3.

The center of Subtropical Storm Joyce at 13/0900 UTC is near
33.8N 43.1W. The estimated minimum central pressure is 1006 mb.
The maximum sustained wind speeds are 40 knots with gusts to 50
knots. Widely scattered moderate convection is from 33N- 36N
between 40W- 44W. A slow southwestward motion is expected for the
next couple of days. A turn toward the northeast with a rapid
increase in forward motion is forecast to occur over the weekend.
Some slight strengthening is forecast during the next 48 hours.
Joyce is forecast to become a tropical storm within the next day
or so. See latest NHC forecast/advisory under AWIPS/WMO headers
MIATCPAT5/WTNT35 KNHC for more details.

Disorganized rainshowers have developed around a western Gulf of
Mexico trough. The system has only about 24 hours of time before
reaching the coast of the western Gulf of Mexico. Upper level
winds in the area of the trough are generally conducive for the
development of a tropical depression. An Air Force Reserve
Hurricane Hunter aircraft is scheduled to investigate the
disturbance later today, if it becomes necessary. Heavy rainfall
and gusty winds are expected across parts of northeastern Mexico,
Texas, and Louisiana on Friday and Saturday. Please monitor the
progress of this system, and refer to bulletins and forecasts
from your local weather office. This system has a medium chance
of tropical cyclone development during the next couple of days.
Please read the latest Tropical Weather Outlook under WMO header
ABNT20 KNHC, and under the AWIPS header MIATWOAT for more details.

...TROPICAL WAVES...

A tropical wave is along 22W/23W, from 20N southward. The wave is
supported by well pronounced 700 mb troughing as depicted in the
GFS model guidance. Scattered moderate convection is within 120 nm
of the wave axis.

...MONSOON TROUGH/ITCZ...

The monsoon trough extends from W Africa near 18N16W to 09N22W to
10N40W. The ITCZ continues from 10N40W to 10N47W to 13N54W.
Widely scattered moderate convection is from 04N-08N between 12W-
30W.

...DISCUSSION...

GULF OF MEXICO...

Please read the SPECIAL FEATURS section, for details about an
area of disturbed weather that is in the southeastern Gulf of
Mexico. A small upper level low is in the N Yucatan Peninsula
near 21N90W, providing further instability over the surface
feature. Scattered showers are now from 20N-27N between 88W-94W.

A stationary front is just inland of the Texas and SW Louisiana
coasts with scattered showers. Isolated moderate convection is
inland, in the SW part of Florida, S of Tampa.

CARIBBEAN SEA...

Isolated moderate rainshowers are in the NW Caribbean Sea and
in Central America W of 84W.

The eastern extent of the eastern Pacific monsoon trough passes
through Costa Rica and Panama along 09N. Scattered moderate
convection is within 120 nm S of the monsoon trough. A 1009 mb low
is centered over N Colombia near 09N75W.

An upper level low is in the SW Caribbean Sea near 13N78W,
enhancing convection.

An an upper level high is centered in the E Caribbean Sea near
17N65W, producing a good amount of shear over T.S. Isaac.

ATLANTIC OCEAN...

Please read the SPECIAL FEATURES section, for details about
Hurricane Florence, Hurricane Helene, and Tropical Storm Isaac.

An upper level cyclonic low is near central Florida, Cocoa Beach,
moving W. Isolated showers and thunderstorms are seen over the W
Atlantic west of 77W to include the NW Bahamas.

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

$$
Formosa/mt
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