[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 151153
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
753 AM EDT Sat Sep 15 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
1145 UTC.

...SPECIAL FEATURES...

Tropical Storm Florence is centered near 33.6N 79.5W at 15/0900
UTC, or 30 nm W of Myrtle Beach South Carolina, moving WSW at 4
kt. Estimated minimum central pressure is 986 mb. Maximum
sustained wind speed is 45 kt with gusts to 55 kt. Scattered
moderate convection is present within 300 nm of the center in the
NE quadrant and within 180 nm of the center in the NW quadrant.
Scattered to numerous moderate convection within an outer
rainband is within 30 nm of a line from 32N78W to 34N77W and to
34.5N77.5W. Latest NHC advisory has Florence to continue with its
slow motion through early today, then is forecast to turn westward
and then northward through the Carolinas and to the Ohio Valley
by Mon. Gradual weakening is forecast while Florence moves farther
inland during the next couple of days, and it is likely to weaken
to a tropical depression by tonight. See the latest NHC
forecast/advisory under AWIPS/WMO headers MIATCPAT1/WTNT31 KNHC
for more details.

Tropical Storm Helene is centered near 37.7N 34.8W at 15/0900 UTC,
or 370 nm W of Lajes Air Base In The Azores, moving NNE at 19 kt.
Estimated minimum central pressure is 988 mb. Maximum sustained
wind speed is 60 kt with gusts to 75 kt. Scattered moderate convection
is seen from 38N to 42N between 32W and 38W. Helene is forecast
by the latest NHC advisory to turn toward the north-northeast
expected by tonight/Sun, passing near or over the Azores. See the
latest NHC forecast/advisory under AWIPS/WMO headers
MIATCPAT3/WTNT33 KNHC for more details.

Tropical Storm Joyce is centered near 31.6N 43.6W at 15/0300 UTC,
or about 900 nm WSW of the Azores moving E at 5 kt. Estimated
minimum central pressure is 997 mb. Maximum sustained winds are
45 kt with gusts to 55 kt. Joyce is being hampered by strong
southwesterly wind shear. Latest satellite imagery shows
scattered moderate convection within 60 nm of the center, and to
the northeast of the cyclone from 32N to 34N, and also within
30 nm of a line from 30N44W to 32N42W. Joyce is forecast by the
latest NHC advisory to turn northeastward with an increase in
forward speed today, with some slight strengthening possible.
Gradual weakening is forecast to begin by Sun. The PUBLIC
ADVISORIES for Joyce are transmitted via the WMO header WTNT3S
KNHC, and via the AWIPS header MIATCPAT5. The FORECAST/ADVISORIES
for Joyce are transmitted via the WMO header WTNT25 KNHC, and via
the AWIPS header MIATCMAT5.

The remnants of Isaac are centered near 14.8N 70.8W at 15/0900
UTC or 230 nm SSW of Santo Domingo Dominican Republic moving W at
14 kt. Estimated minimum central pressure is 1006 mb. Maximum
sustained wind speed is 30 kt with gusts to 40 kt. Scattered
moderate convection is noted from 14N-18N between 64W-74W
affecting the adjacent waters of south of Puerto Rico and
Hispaniola. See the last NHC forecast/advisory under AWIPS/WMO
headers MIATCPAT4/WTNT34 KNHC for more details.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis along 30W from
01N to 21N, moving westward at 10 kt. The wave is surrounded by a
rather dry environment, which is inhibiting deep convection from
forming along or near it. Only isolated showers are within 120 nm
either side of the wave axis where it crosses the monsoon trough.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from off the coast of Guinea
Bissau, Africa to 09N25W to 08N32W. The ITCZ continues from
08N32W to 09N41W to 10N46W to 12N57W. Aside from the shower and
thunderstorm activity associated with the tropical wave along 30W,
scattered moderate isolated strong convection is within 180 nm
south of the ITCZ from 41W and 54W. Scattered moderate convection
is within 180 nm south of the monsoon trough from 21W to 25W, and
also well south of the monsoon trough from 04N to 09N between
15W and 18W.

...DISCUSSION...

GULF OF MEXICO...

An upper-level cyclonic circulation center is over the north-
central gulf near 26N90W, with an inverted trough to an upper low
over the northwestern Caribbean at 20N84W that is moving
westward. Upper-level cyclonic wind flow covers the central part
of the gulf. A surface trough extends from just inland central
near Freeport southwestward to a 1009 mb low near Baffin Bay and
to Ciudad Camargo and to northeastern Mexico near Ciudad Mante.
Both satellite imagery and NWS doppler radar imagery depict
increasing scattered moderate to strong convection that is
becoming more concentrated over and just inland the Texas coast
from Brownsville to just south of Corpus Christi, and eastward
from these two locations to near 95W. This activity is rotating
in a cyclonic fashion around the low as the trough/low system
slowly moves further inland through today and this evening. The
activity will likely produce heavy rainfall and possible strong
gusty winds as well. Scattered showers and thunderstorms are
over northeastern Mexico. Scattered showers and isolated
thunderstorms are elsewhere south of 28N and west of 92W.
Isolated showers are possible east of 92W.

A weak ridge extends northwest to southeast from SE Louisiana to
Florida Bay will shift slightly south on Sun with the ridge
extending southeast to the Yucatan Basin. A weak surface trough,
extending southwest from the remnants of tropical cyclone
Florence, will pass slowly east across the north-central gulf
waters through early next week.

CARIBBEAN SEA...

Please refer to the Special Feature section above for details on
Isaac.

An upper level cyclonic circulation center is about 100 nm to the
west of Jamaica, in the NW corner of the Caribbean Sea. Isolated
showers and thunderstorms are north of 15N and west of 80W.

Tropical Storm Isaac near 15.4N 69.5W 1002 mb at 0300 UTC is
moving W at 13 kt. Maximum sustained winds 35 kt gusts 45 kt.
Isaac will move more west-northwest and reach near 15.7N 73.3W
Sat evening, then gradually weaken to a tropical depression near
16.7N 77.4W Sun evening, before shifting NW and dissipating by
late Mon. Otherwise, gentle to moderate trades are forecast west
of Isaac, while moderate to locally fresh trades are forecast to
the east of Isaac. Strong nocturnal trades are forecast off the
northwest coast of Colombia on Mon and Tue nights.

ATLANTIC OCEAN...

Please refer to the Special Features section above, for details
on Florence, Helene, and Joyce.

An upper-level trough extends from near 32N45W to 26N48W to
20N54W, and to 16N59W. Upper-level cyclonic wind flow is within
360 nm on either side of the trough. Scattered showers and
isolated thunderstorms are within 30 nm ether side of a line
from 22N45W to 22N51W to 22N55W. Isolated showers and
thunderstorms are seen elsewhere to the west of 56W.

A cyclonic shear axis north of the area near 34W from 50W to 63W
is dropping southward. Multilayer clouds with embedded scattered
showers and isolated thunderstorms are noted north of 30N
between 53W and 63W.

A surface ridge will remain about stationary from near 32N68W to
southeastern Florida through Sun. The ridge will shift
northward, to a position from near 32N74W to central Florida by
the middle of the next week.

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

$$

JA/ERA

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