[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 130723
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
323 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 0000 UTC surface analysis and satellite imagery through
0515 UTC.

...SPECIAL FEATURES...

Hurricane Florence centered near 32.5N 74.3W at 13/0600 UTC or
200 nm ESE of Wilmington North Carolina moving NW at 15 kt.
Estimated minimum central pressure is 956 mb. Maximum sustained
wind speed is 95 kt with gusts to 115 kt. Scattered moderate to
strong convection is from 30N-35N between 69W-76W. The present NW
motion of Florida 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 15.3N 58.0W at 13/0300 UTC or
190 nm E of Dominica moving W at 17 kt. Estimated minimum
central pressure is 1006 mb. Maximum sustained wind speed is 45
kt with gusts to 55 kt. 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 22.4N 36.9W at 13/0300 UTC or
1100 nm SSW of Lajes Air Base In The Azores moving N at 11 kt.
Estimated minimum central pressure is 983 mb. Maximum sustained
wind speed is 70 kt with gusts to 85 kt. 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.

Subtropical Storm Joyce centered near 34.1N 42.6W at 13/0300 UTC
or 790 nm WSW of the Azores moving SW at 5 kt. Estimated minimum
central pressure is 1006 mb. Maximum sustained wind speed is 40
kt with gusts to 50 kt. 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.

A broad area of low pressure is located over the central Gulf of
Mexico near 24N92W. Although the shower activity is still
disorganized, upper level winds are forecast to become more
conducive for development, and it is likely that a tropical
depression will form Thursday or Thursday night, before the system
reaches the western Gulf coast. An Air Force Reserve Hurricane
Hunter aircraft is scheduled to investigate the disturbance
tomorrow, if necessary. Regardless of development, heavy rainfall
and gusty winds are expected across portions of northeastern
Mexico, Texas, and Louisiana late this week. This system has a
high chance of tropical cyclone development over 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 on this evolving system.

...TROPICAL WAVES...

A tropical wave is off the coast of W Africa along 21W south of
20N, moving W at 10 kt. 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 09N21W to
10N41W. the ITCZ continues from 10N41W to 10N49W to 13N53W. Widely
scattered moderate convection is from 04N-08N between 12W-30W.

...DISCUSSION...

GULF OF MEXICO...

See Special Features above for details on an area of disturbed
weather over the southeastern Gulf of Mexico. A small upper level
low is centered over the N Yucatan Peninsula near 21N90W
providing further instability over the surface feature. Scattered
showers are now from 20N-27N between 88W-94W. Further N, a
stationary front is just inland of the Texas and SW Louisiana
coasts with scattered showers. Elsewhere, isolated moderate
convection is inland over the SW portion of the Florida Peninsula,
S of Tampa.

CARIBBEAN SEA...

Isolated moderate convection is over the NW Caribbean and Central
America W of 84W. Further S, the eastern extent of the eastern
Pacific monsoon trough is over 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.

In the upper levels, an upper level low is centered over the SW
Caribbean near 13N78W enhancing convection. Further E, an upper
level high is centered over the E Caribbean near 17N65W producing
a good amount of shear over T.S. Isaac.

ATLANTIC OCEAN...

Please refer to the Special Features section above for details
on Hurricanes Florence and Helene and on Tropical Storm Isaac.

In the upper-levels, a small upper level low is centered over
central Florida near Cocoa Beach at 29N81W, 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
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