[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 121754 AAA
TWDAT

Tropical Weather Discussion...Updated
NWS National Hurricane Center Miami FL
154 PM EDT Wed Sep 12 2018

Updated Special Features for Isaac latest 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
1700 UTC.

...SPECIAL FEATURES...Updated

Hurricane Florence is centered near 29.4N 70.7W at 12/1200 UTC or
about 460 nm SE of Cape Fear, North Carolina moving WNW or 300
degrees at 15 kt. Estimated minimum central pressure is 943 mb.
Maximum sustained winds have diminished a little to 115 kt with
gusts to 140 kt. Latest satellite imagery continues to show a
rather distinct eye feature with Florence. Numerous strong
convection is within 90 nm of the center in the S semicircle and
60 nm of the center in the NE quadrant. Scattered moderate to
isolated strong convection is within 60 nm of the center in the NW
quadrant and elsewhere within 150 nm of the center in the NE
quadrant. Scattered moderate convection is seen from 30N to 32N
between 68W and 73W. A motion toward the west-northwest and
northwest is expected through early Thu. Florence is expected to
slow down considerably by late Thu into Friday. On the forecast
track, the center of Florence will move over the southwestern
Atlantic Ocean between Bermuda and the Bahamas through Wed, and
approach the coast of North Carolina or South Carolina in the
hurricane warning area on Thu and Fri. Florence is a category 4
hurricane on the Saffir- Simpson Hurricane Wind Scale. Further
strengthening is forecast through tonight. While some weakening is
expected on Thu, Florence is forecast to be an extremely
dangerous major hurricane through landfall. 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 is centered near 14.4N 54.1W at 12/1200 UTC
or 390 nm E of Martinique moving W or 270 degrees at 13 kt.
Estimated minimum central pressure is 1000 mb. Maximum sustained
winds are 55 kt with gusts to 65 kt. Latest satellite imagery
shows numerous strong convection within 60 nm of the center in
the NE and SE quadrants. Scattered moderate to strong convection
is elsewhere within 150 nm of the center in the NE quadrant, and
within 120 nm of the center in the SE quadrant. Scattered
moderate convection is from 13N to 15N between 50W and 51W. On
the present forecast track, Isaac is forecast to move across the
central Lesser Antilles and into the eastern Caribbean Sea on
Thu, and move into the eastern Caribbean Sea Thu night, and into
the central Caribbean Sea by Fri or Sat. Gradual weakening is
forecast during the next few days. 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 is centered near 19.2N 35.7W at 12/0900 UTC or
about 700 nm WNW of the Cabo Verde Islands and about 1220 nm
SSW of the Azores. It is moving WNW at 11 kt. Estimated minimum
central pressure is 977 mb. Maximum sustained winds have
diminished slightly to 80 kt with gusts to 100 kt. Latest
satellite imagery shows scattered moderate to strong convection
within 150 nm of the center in the NW quadrant, and within 120 nm
of the center in the SW quadrant. Scattered moderate isolated
strong convection within 150 nm of center in the NE quadrant and
within 90 nm of the center in the SE quadrant. Helene is forecast
to turn toward the north today, before a turn toward the NE
with an increase in forward speed occurs by the end of the week.
Helen is forecast to weaken to a tropical storm on Thu. 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.

Cloudiness and showers associated with a trough of low pressure
over the south-central Gulf of Mexico have decreased since
yesterday and the Air Force reconnaissance plane scheduled to
investigate the system for today will likely be cancelled.
However, upper-level winds are forecast to become a little more
conducive for development, and a tropical depression could still
form on Thu or Fri before the system reaches the western Gulf
Coast. This system has a high chance of tropical cyclone
development over the next couple of days. Regardless of
development, heavy rainfall and gusty winds are expected across
portions of northeastern Mexico, Texas, and Louisiana late this
week, and interests there should monitor the progress of this
system. 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.

A non-tropical area of low pressure located several hundred
miles west-southwest of the Azores is producing a large area of
showers and thunderstorms and gale-force winds. This system could
gradually acquire tropical or subtropical characteristics during the
next couple of days while it meanders over the northeastern Atlantic
Ocean, and before it becomes absorbed by a larger trough of low
pressure. Latest satellite imagery shows scattered moderate
convection within 210 nm of the center in the SE quadrant, and
within 120 nm of the center in the SW quadrant. Similar convection
is from 34N to 40N between 31W and 41W. This system has a
medium chance for tropical or subtropical cyclone development
over the next 48 hours. For more information, see High Seas
Forecasts issued by the National Weather Service. Please read the
latest Tropical Weather Outlook under WMO header ABNT20 KNHC, and
under the AWIPS header MIATWOAT for updates on the chances for
development of this system.

...TROPICAL WAVES...

A new tropical wave has its axis just offshore the west coast of
Africa along 17W from 03N to 19N, moving westward at 10 to 15 kt.
The wave is supported by well pronounced 700 mb troughing as
depicted in the GFS model guidance. Scattered moderate isolated
strong convection is seen within 120 nm either side of the wave
axis from 16N to 19N. Scattered moderate convection is occurring
within 120 nm west of the wave axis from 08N to 10N, and within
60 nm east of the wave axis from 10N to 13N.

...MONSOON TROUGH/ITCZ...

The monsoon trough extends from W Africa near 11N15W to 06N17W to
04N22W. Scattered moderate convection is within 30 nm of the
trough between 17W and 22W. Similar convection is north of the
monsoon trough within 60 nm of a line from 09N19W to 09N23W, and
within 30 nm of a line from 08N23W to 08N29W.

...DISCUSSION...

GULF OF MEXICO...

See Special Features above for details on an area of disturbed
weather over the southeastern Gulf of Mexico.

In the upper-levels, a nearly stationary upper-level low is
centered near 22N88W, with a trough extending southward to over
the eastern Yucatan Peninsula. Scattered moderate to strong
convection is from 24N to 26N between 88W and 92W. A surface
trough is analyzed from near 27N87W to a 1010 mb low at 23N88W
and to inland the central Yucatan Peninsula to northern
Guatemala. Scattered moderate convection is noted from 23N to
25N between 83W and 85W. Scattered showers and isolated
thunderstorms are elsewhere south of 28N east of 87W, and also
south of 27N between 87W and 92W.

A stationary front is just inland the Texas coast. Scattered
showers and thunderstorms are present from 19N to 2&N west of
95W.

CARIBBEAN SEA...

In the upper-levels, a nearly stationary upper-level low is
centered near 22N88W, with a trough extending southward to over
the eastern Yucatan Peninsula.  Upper-level diffluence over a
very moist and unstable environment is helping to sustain
scattered moderate to strong convection from 16N to 21N west of
86W. Isolated showers and thunderstorms are elsewhere north of
15N west of 71W and east of 71W.

The eastern extent of the eastern Pacific monsoon trough is over
Costa Rica and Panama along 09N. Isolated showers and
thunderstorms are within 60 nm S of the monsoon trough. A 1009
mb low is centered over N Colombia near 09N74W.

In the upper-levels, an upper level low is centered over
nnorthwestern  Colombia near 12N73W. An upper level anticyclone is
centered just E of the Leeward Islands near 16N59W.

Tropical Storm Isaac centered near 14.5N 53.5W 1000 mb at 5 AM
EDT is moving W at 13 kt. Maximum sustained winds are 50 kt with
gusts to 60 kt. Isaac will move across the Lesser Antilles on
Thursday, and expected to weaken through Fri night. High winds and
rough seas, primarily north of the center, will accompany the
tropical storm as it moves across the region.

ATLANTIC OCEAN...

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

Scattered showers are over the central Atlantic N of 29N between
40W and due to a cold front N of the area.

In the upper-levels, a small upper level low is centered N of the
Bahamas near 29N78W. Isolated showers and thunderstorms are over
and near the NW Bahamas.

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

$$
Formosa/Aguirre
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