[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 141148
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
748 AM EDT Fri Sep 14 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
1100 UTC.

...SPECIAL FEATURES...

Hurricane Florence centered near 34.2N 77.4W at 14/0900 UTC or 20
nm E of Wilmington North Carolina moving WNW at 5 kt. Estimated
minimum central pressure is 958 mb. Maximum sustained wind speed
is 80 kt with gusts to 100 kt. Numerous moderate and scattered
strong convection is present within 60 nm in the NE semicircle and
within 30 nm in the SW semicircle. Scattered moderate and
isolated strong convection is found elsewhere within 180 nm of the
center. A turn toward the W at a slow forward speed is expected
today, followed by a slow WSW motion tonight and Saturday. On this
forecast track, the center of Florence is expected to move inland
across extreme southeastern North Carolina and extreme eastern
South Carolina today and Saturday. Florence will then move
generally northward across the western Carolinas and the central
Appalachian Mountains early next week.

Maximum sustained winds remain near 90 mph (150 km/h) with higher
gusts. Gradual weakening is forecast later today and tonight.
Significant weakening is expected over the weekend and into early
next week while Florence moves farther 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 Helene centered near 30.6N 36.0W at 14/0900 UTC or
660 nm SW of Lajes Air Base In The Azores moving N at 20 kt.
Estimated minimum central pressure is 992 mb. Maximum sustained
wind speed is 55 kt with gusts to 65 kt. Scattered moderate
convection is observed in the NW semicircle within 150 nm. Helene
is expected to turn NE over the weekend. On this forecast track,
Helene will pass near or over the Azores late Saturday or Sunday.

Maximum sustained winds are near 65 mph (100 km/h) with higher
gusts. Little change in strength is forecast during the next 48
hours. Gradual weakening is expected after Helene becomes a post-
tropical cyclone over the weekend.

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 Storm Joyce centered near 32.1N 44.9W at 14/0900 UTC or
950 nm WSW of the Azores moving SSW at 7 kt. Estimated minimum
central pressure is 1003 mb. Maximum sustained wind speed is 35 kt
with gusts to 45 kt. Scattered moderate convection is seen from
32N to 35N between 43W and 45W. Joyce is interacting with Tropical
Storm Helene and as a result is moving toward the SSW near 8 mph
(13 km/h). Joyce is forecast to slow down and turn eastward by
tonight, and then accelerate northeastward over the weekend.

Maximum sustained winds are near 40 mph (65 km/h) with higher
gusts. Little change in strength is forecast during the next
couple of days. Joyce is expected to weaken early next week. See
latest NHC forecast/advisory under AWIPS/WMO headers
MIATCPAT5/WTNT35 KNHC for more details.

Newly downgraded Tropical Depression Isaac centered near 15.0N
65.5W at 14/0900 UTC or 170 nm SSW of St. Croix moving W at 13 kt.
Estimated minimum central pressure is 1006 mb. Maximum sustained
wind speed is 30 kt with gusts to 40 kt. Numerous moderate and
scattered strong convection is present within 60 nm of 16N65W.
Scattered moderate and isolated strong convection is taking place
elsewhere from 12N to 17N between 60W and 67W. A westward motion
with a decrease in forward speed is expected during the next few
days. On the forecast track, Isaac will move over the eastern and
central Caribbean Sea during the next few days. Isaac is forecast
to gradually weaken, and could degenerate into a tropical wave at
any time. 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.

Shower coverage and organization in association with a broad area
of low pressure located over the western Gulf of Mexico have
changed little during the past 6 hours. Although upper-level winds
appear conducive for development, this system has only a short
period of time to develop into a tropical depression before it
moves inland over northeastern Mexico and southern Texas later
today. Numerous moderate and scattered strong convection are
present within 60 nm of 24.5N96.5W. Scattered moderate and
isolated strong convection are observed elsewhere from 18N to 29N
W of 92W. Regardless of development, heavy rainfall and gusty
winds are expected across portions of NE Mexico and Texas later
today and Saturday. 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 has an axis extending from 05N28W to 20N28W,
moving W around 15 kt. The wave is embedded in an area of abundant
moisture as indicated in TPW satellite imagery and coincides with
well pronounced 700 mb troughing depicted in the GFS model
guidance. Scattered moderate and isolated strong convection is
taking place from 07N to 11N between 28W and 35W.


...MONSOON TROUGH/ITCZ...

The monsoon trough extends from Mauritania in W Africa near
18N16W to 11N22W to 08N32W. The ITCZ continues from 08N32W to
10N48W to 15N60W. Aside from the convection associated with the
tropical wave near 28W, scattered moderate and isolated strong
convection is occurring from 05N to 07N between 16W and 21W.

...DISCUSSION...

GULF OF MEXICO...

Please refer to the SPECIAL FEATURES section for details about an
area of disturbed weather that lies over the western Gulf of
Mexico. Otherwise, broad upper-level ridging extends across the
northern Gulf. A weak upper-level low is centered over the NE Gulf
near 29N85W. There is no significant convection currently
associated with this feature. Once the area of disturbed weather
moves W of the Gulf, deep-layer ridging is expected to maintain a
quiet weather pattern and light winds over the basin for the next
few days.

CARIBBEAN SEA...

Please refer to the the SPECIAL FEATURES section for details
about Tropical Storm Isaac.

The eastern Pacific monsoon trough passes through Costa Rica and
Panama along 09N to low pres 1008 mb centered over Colombia near
09N75W. Scattered moderate convection is found S of 12N between
76W and 81W. A weak upper-level low possessing no significant
deep convection is centered the western Caribbean Sea near 17N82W.

The high pressure ridge over the western Atlc has been weakened
by Hurricane Florence. As a result, winds will be generally light
to moderate over the portion of the basin away from the influence
of T.D. Isaac.


ATLANTIC OCEAN...

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

The features mentioned above are combining to weaken the ridge
over the Atlantic. As a result, light to moderate trades are
generally expected over the basin W of 35W through Sat night.
Winds will strengthen next week as the ridge rebuilds.

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

$$
McElroy
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