[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 110005
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
805 PM EDT Mon Sep 10 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 1800 UTC surface analysis and satellite imagery through
2345 UTC.

...SPECIAL FEATURES...

The center of Hurricane Florence at 10/2100 UTC is near 25.4N
61.1W. Florence is moving WNW, or 285 degrees, 11 knots. The
estimated minimum central pressure is 939 mb. The maximum
sustained wind speeds are 120 knots with gusts to 145 knots.
Scattered moderate to strong rainshowers are within 30 nm of the
center everywhere. People who are in the SE part and the Mid-
Atlantic states of the U.S.A. should monitor the progress of
FLORENCE. It is possible that storm surge and hurricane watches
may be issued for parts of these areas by Tuesday morning.
Numerous strong rainshowers are within 90 nm of the center in the
NW semicircle. Scattered moderate to isolated strong rainshowers
are elsewhere from 21N to 28N between 54W and 62W. 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.

The center of Hurricane Isaac at 10/2100 UTC is near 14.4N 45.0W.
Isaac is moving W, or 270 degrees, 12 knots. The estimated
minimum central pressure is 993 mb. The maximum sustained wind
speeds are 65 knots with gusts to 80 knots. People who are in the
Lesser Antilles should monitor the progress of ISAAC.
Numerous strong rainshowers are within 75 nm of the center in the
W semicircle, and within 45 nm of the center in the E semicircle.
Scattered moderate to strong rainshowers are from 12N to 14N
between 41W and 44W. Anyone who is in the area of the Lesser
Antilles should monitor the progress of Hurricane Isaac. 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.

The center of Hurricane Helene at 10/2100 UTC is near 14.9N
31.5W. Helene is moving WNW, or 290 degrees, 12 knots. The
estimated minimum central pressure is 974 mb. The maximum
sustained wind speeds are 90 knots with gusts to 110 kt. Numerous
strong rainshowers are within 135 nm of the center in the NW
quadrant and in the SW quadrant. Widely scattered moderate to
isolated strong rainshowers are elsewhere from 09N to 17N between
22W and 31W. 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.

...TROPICAL WAVES...

No tropical wave is present at this time.


...MONSOON TROUGH/ITCZ...

The monsoon trough is inland in Africa. The ITCZ is not analyzed
at this time. along 08N48W 06N54W 07N58W. Isolated moderate to
locally strong rainshowers are elsewhere from 10N southward from
20W eastward, and to the south of Hurricane Isaac and Hurricane
Helene from 06N to 10N between 34W and 45W. Rainshowers are
possible elsewhere from 10N southward from 60W eastward.

...DISCUSSION...

GULF OF MEXICO...

An upper-level trough extends from the NE corner of the Gulf of
Mexico, to the east central Gulf of Mexico, to a cyclonic
circulation center that is just to the north of the Yucatan
Peninsula. Upper level cyclonic wind flow covers the Gulf of
Mexico east of 92W. Upper level anticyclonic wind flow covers the
rest of the area. Widely scattered moderate to isolated strong
rainshowers are to the east of 90W. This area of precipitation is
forecast to move slowly northwestward near the Yucatan Peninsula
on Tuesday with limited development expected. Upper level winds
are forecast to become more conducive for development on
Wednesday, when the system moves across the southern Gulf of
Mexico. It is possible that a tropical depression may form on
Thursday or Friday, while the disturbance moves across the
western Gulf of Mexico. Please read the latest Tropical Weather
Outlook for more details, TWOAT/ABNT20 KNHC.

A frontal trough is in the Texas coastal plains/the Texas coastal
waters. Isolated moderate rainshowers are to the west of the line
that runs from SE Louisiana to the coast of Mexico near 20N96W.

A surface trough in the western Caribbean will move
across the Yucatan peninsula Tue, and into the Gulf of Mexico Wed.
The trough will move into the western gulf Thu, and west of the
area Sat.

CARIBBEAN SEA...

Upper-level cyclonic flow associated with the upper low over the
Gulf of Mexico near 25N88W covers the northwestern Caribbean Sea
as well as western and central Cuba. A weak surface trough is
analyzed from near 21N82.5W to near just northeast of the
northeastern coast of Honduras. Scattered moderate to strong
convection increasing in coverage is observed to the north of
17N west of 79W to juts inland the coast of the Yucatan
Peninsula. This activity is quickly lifting northward under
moderate to strong upper-level southerly flow located to the east
of the Gulf of Mexico upper-level low near 25N88W. Satellite
imagery indicates that this activity is showing signs of
organization, and it is forecast to move slowly northwestward
near the Yucatan Peninsula on Tue with limited development
expected. Upper-level winds are forecast to become more
conducive for development on Wed when the system moves over the
southern Gulf of Mexico.

Rainshowers that are in NW corner of the Caribbean Sea, western
Cuba, the Yucatan Peninsula of Mexico, and Central America from
Honduras to El Salvador and Guatemala, are associated with a
surface trough, and are showing some signs of organization. This
system is forecast to move slowly northwestward across the Yucatan
Peninsula on Tuesday with limited development. Upper level winds
are forecast to become more conducive for development later in the
week. It is possible that a tropical depression may form on
Thursday or Friday, while the disturbance moves across the
western Gulf of Mexico. People who are in NE Mexico and the coast
of Texas and Louisiana should monitor the progress of this
system. It is likely that heavy rainfall and gusty winds will be
present in western Cuba and the Yucatan Peninsula through
Tuesday.

Hurricane Isaac near 14.4N 45.0W 993 mb at 5 PM EDT
moving W at 12 kt. Maximum sustained winds 65 kt gusts 80 kt.
Isaac will move to 14.5N 47.1W Tue morning, 14.6N 49.8W Tue
afternoon, 14.6N 52.3W Wed morning, 14.8N 54.7W Wed afternoon, and
15.3N 60.2W Thu afternoon. Isaac will weaken to a tropical storm
near 15.5N 65.5W Fri afternoon, and change little in intensity as
it moves to 15.5N 70.5W Sat.

ATLANTIC OCEAN...

Please read the SPECIAL FEATURES section for details about
Hurricane FLORENCE, Hurricane ISAAC, and Hurricane HELENE.

A surface trough is analyzed from 32N61W to 29N65W. Upper-level
cyclonic flow is present to the north of 27N between 67W and 74W
attributed to an upper low moving westward near 29N74W. Broad
anticyclonic is west of 74W due to the upper-level low in the
Gulf of Mexico near 24N88W. Water vapor imagery shows mid to
upper-level clouds streaming northeastward and eastward over the
western half of the area. These clouds are originating from the
deep convective activity that is occurring over the southeastern
Gulf of Mexico as described above. Otherwise, isolated showers
and thunderstorms are west of 65W.

A weak 1017 mb high center is analyzed at 26N73W, with a ridge
southwestward to the Straits of Florida. The associated weak
gradeint is allowing for generally light to gentle winds to
exist over the western half of the area. Expect for these
conditions to continue through Wed, except in the northeastern
section the the TAFB forecast offshore waters zones where
Hurricane Florence is forecast to track across. Below is
the latest forecast for Florence bases on the 15Z NHC advisory.

Hurricane Florence near 25.4N 61.1W 939 mb at 5 PM
EDT moving WNW at 11 kt. Maximum sustained winds 120 kt gusts 145
kt. Florence will move to 26.0N 63.2W Tue morning, 27.0N 66.2W Tue
afternoon, 28.6N 69.3W Wed morning, 30.4N 72.2W Wed afternoon,
and move north of the area to near 33.7N 77.0W Thu afternoon.

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

$$
ja/al/mt
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