[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 101805
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
805 AM 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 1200 UTC surface analysis and satellite imagery through
1745 UTC.

...SPECIAL FEATURES...

Hurricane Florence is centered near 24.9N 58.9W at 10/1500 UTC
or 540 nm SE of Bermuda and about 1080 nm ESE of Cape Fear North
Carolina moving W or 280 degrees at 12 kt The estimated minimum
central pressure is 962 mb. The maximum sustained wind speeds
have increased to 100 kt with gusts to 120 kt. Florence is
continues to rapidly strengthening. Latest satellite imagery
shows a very distinct eye feature, about 10 nm in diameter. The
imagery shows scattered moderate convection within 90 nm NE of
the eye in the NE quadrant, within 60 nm of the eye in the NW
quadrant, within 60 nm of the eye in the SW quadrant and within
30 nm of the eye in the SE quadrant.  Scattered moderate
isolated strong convection is elsewhere within 180 nm of the eye
in the NE quadrant and within 150 nm of the eye in the SE
quadrant. Scattered moderate isolated strong convection is
elsewhere within 120 nm of the eye in the W semicircle. Latest
NHC advisory has Florence continuing to strengthen as it tracks
in west- northwest motion during the next couple of days, before
an expected turn to the northwest occurs on Wed night. 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.

Hurricane Isaac is centered near 14.7N 43.9W at 10/1500 UTC,
which is about 1000 nm E of the Windward Islands, moving or 275
degrees at 12 kt. The estimated minimum central pressure is 993
mb. The maximum sustained wind speeds are 65 kt with gusts to 80
kt. Latest satellite imagery shows that Issac's overall cloud
pattern appears ragged.  Isaac remains a small hurricane, with
scattered moderate to numerous strong convection within 90 nm of
the center in the N and SW, and within 60 nm of the center in
the SE quadrant. Scattered moderate isolated strong convection
is within 120 nm of center in the NE quadrant and within 60 nm
of the center in the SE quadrant. An outer rainband is denoted
by scattered moderate convection within 30 nm of a line from
12N46W to 14N45W. The latest NHC advisory forecasts a westward
motion, with a slight increase in forward speed the through the
end of the week. 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 14.6N 30.0W at 10/1500 UTC,
which is about 330 nm W of the southernmost Cabo Verde Islands,
and is moving WNW or 285 degrees at 15 kt. The estimated minimum
central pressure is 984 mb. The maximum sustained wind speeds
are 75 knots with gusts to 90 kt. Latest satellite imagery shows
scattered moderate to numerous strong convection within 120 nm
of the center in the NE, SE and S quadrants, and within 90 mm
elsewhere of the center. Latest NHC advisory forecasts Helene to
continue its present motion through late Tue, with a decrease in
its forward motion, followed by a turn to the northwest and then
to the north-northwest on Wed and Thu. Latest satellite imagery
shows scattered moderate convection within 90 nm of the center
in the SE quadrant and within 60 nm of the center in the SW
quadrant. Scattered moderate convection is elsewhere within 270
nm of the center in the SW, within 210 nm of the center in the
SE quadrant and within 120 nm of the center in the northern
semicircle. 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...

The previous tropical wave that was along 92W is has moved to
over the far eastern Pacific, with its northern portion over
southeastern Mexico. Scattered moderate is over far eastern
Mexico from 17N to 19N between 91W and 93W. Isolated showers and
thunderstorms are over the Pacific waters near Guatemala and the
Isthmus of the Gulf of Tehuantepec of southern Mexico between
92W and 95W.

...MONSOON TROUGH/ITCZ...

The monsoon trough is analyzed over inland Africa. The ITCZ
extends from 08N48W to 07N58W. Isolated moderate convection is
within 60 nm N of the ITCZ between 54W and 58W.

...DISCUSSION...

GULF OF MEXICO...

An upper-level trough extends from the NE corner of the Gulf of
Mexico, to an elongated upper-level low at 25N88W and
southwestward to the Yucatan Peninsula. Associated upper-level
cyclonic flow covers the Gulf of Mexico east of about 94W, while
upper-level anticyclonic flow is west of 94W. Isolated showers
and thunderstorms are noted over just about the entire basin,
except for scattered moderate isolated strong convection from
24N to 30N west of 94W, and over the southeastern gulf where
upper divergence east of the upper low is helping to sustain
increasing scattered moderate isolated strong convection there.
This convection is spreading northward across the southeastern
gulf and over much of the Straits of Florida from the
northwestern Caribbean Sea. Strong gusty winds can be expected
with this activity. This area of convection 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, and a tropical
depression could form on Thu or Friday while the disturbance
moves across the western Gulf of Mexico. Please refer to the
latest Tropical Weather Outlook for the latest information on
this system.

The gradient associated with a weak high pressure over the
southeastern United States will maintain light to moderate winds
over the basin through Fri night. A surface trough will move
westward, off the coast of the Yucatan Peninsula each evening,
and it will dissipate in the SW Gulf of Mexico each morning. The
trough will be accompanied by moderate to fresh winds.

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 21N82W to near just northeast of the
northeastern coast of Honduras. Scattered moderate to strong
convection is increasing from north of 15N to over Cuba between
79W and 85W, as well as over the Yucatan Channel. This activity
is quickly lifting northward under moderate to strong upper flow
located to the southeast of the Gulf of Mexico upper-level low.
In addition, this activity is showing some signs of
organization. The overall area of shower and thunderstorms
activity 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.

Isolated showers and thunderstorms are elsewhere west of 78W.

A relatively weak surface ridge in the western Atlantic Ocean
will maintain moderate to fresh trade winds over most of the
region through Thu, except over the far eastern Caribbean where
winds are expected to increase as Hurricane Isaac, near 14.6N
30.0W at 15 UTC, approaches that part of the Caribbean from the
tropical Atlantic waters. Please refer to the latest advisory on
Isaac for further details on its track and intensity.

ATLANTIC OCEAN...

Please see the Special Features section for details about
Hurricane Florence, Hurricane Isaac, and Hurricane Helene.

An upper level cyclonic circulation center is near 29N70W. A
surface trough is along 36N61W 34N62W 31N64W. Upper level
cyclonic wind flow also is from 30N northward from 77W westward.
Isolated moderate rainshowers are from 26N northward from 69W
westward.

Hurricane Florence near 25.0N 60.0W 962 mb at 11 AM EDT moving W
at 11 kt. Maximum sustained winds 100 kt gusts 120 kt. Florence
will move to 25.5N 61.9W this evening, 26.4N 64.7W Tue morning,
27.8N 67.9W Tue evening, 29.5N 71.0W Wed morning, north of the
area near 33.0N 76.3W Thu morning.

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

$$
Aguirre
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