[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 070542
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
142 AM EDT Fri Sep 7 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 0000 UTC surface analysis and satellite imagery through
0545 UTC.

...SPECIAL FEATURES...

Recently downgraded Tropical Storm Florence is centered near
25.1N 49.8W at 07/0300 UTC, which is about 900 nm east-northeast
of the northern Leeward Islands or 915 nm east-southeast of
Bermuda. It is moving WNW or 290 degrees at 6 kt. The estimated
minimum central pressure is 993 mb. Maximum sustained winds have
diminished to 60 kt with gusts to 75 kt. Latest satellite imagery
shows that the cyclone has been undergoing southwesterly vertical
upper-level shear as noted by its tilted NE to SW cloud pattern.
The imagery also shows what appears to be the low-level center
exposed on the southwest side of the cyclone's deep convection.
The deep convection consists of the scattered moderate isolated
strong type intensity from 25N to 28N between 45W and 48W. Similar
convection is within 60 nm NE of the center of Florence. The
latest NHC forecast calls for Florence to move northwestward
through tonight before it turns toward to the west on Fri. It is
forecast to weaken slightly today, then re-strengthen beginning
this evening and through the upcoming weekend. See latest NHC
forecast/advisory under AWIPS/WMO headers MIATCPAT1/WTNT31 KNHC
for more details.

A broad and elongated area of low pressure is centered several
hundred miles west-southwest of the Cabo Verde Islands is denoted
by a tropical wave with its axis along 33W and extending from 04N
to 20N. A 1008 mb low is on the wave axis near 14N33W. This
system is moving westward at 10 to 15 kt. The associated shower
and thunderstorm activity has increased some during the last
couple of hours. Latest satellite imagery shows scattered
moderate to strong convection within 150 nm of the low in the W
quadrant. Scattered moderate convection is to the NE of the low
within 30 nm of 16N31W, and well west of the low from 12N to 14N
between 36W and 38W. Environmental conditions appear conducive
for development, and a tropical depression is expected to form
within the next day or two while the system moves slowly westward
across the tropical Atlantic. The chance of this system becoming
a tropical cyclone during the next 48 hours remains in the high
range. Please read the latest NHC Tropical Weather Outlook under
AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more information.

A tropical wave just inland along the coast of western Africa has
its axis near 16W from 04N to 20N, with a 1007 mb low on the axis
near 13N16W. This system is moving westward at 10 to 15 kt.
Latest satellite long term animation indicates that this system is
exhibiting signs of organization. Very large clusters of
numerous strong convection have significantly increased in
advance of this system as observed from the coastal sections of
Senegal to Sierra Leone, and westward from these locations to 19W.
This activity also spreads eastward to within 90 to 120 nm inland
the coast of Africa. Environmental conditions appear conducive for
development, and a tropical depression or tropical storm is likely
to form later today or over the upcoming weekend while the wave
and low moves westward or west-northwestward over the far eastern
tropical Atlantic Ocean. The chance of this system becoming a
tropical cyclone during the next 48 hours is now in the high
range. Interests in the Cabo Verde Islands should monitor the
progress of this system, and advisories on a potential tropical
cyclone or tropical depression could be issued later today.
Please read the latest NHC Tropical Weather Outlook under
AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more information.

...TROPICAL WAVES...

A tropical wave has its axis along 80W/81W south of 20N, moving
westward at 10 to 15 kt. Scattered moderate convection is
within 60 nm of the wave from 15N to 20N. Isolated showers and
thunderstorms are elsewhere within 60 to 120 nm either side of
the wave.

A tropical wave has its axis along 94W and south of 21N, and
continues southward across southeastern Mexico and the Isthmus of
Tehuantepec and further southward to the eastern Pacific near
04N. It is moving westward near 15 kt. Only isolated showers are
seen within 60 nm of the wave axis.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from well inland Africa to the
1007 mb low that is associated with the tropical wave along 16W,
and continues from this low to 14N25W to the low 1008 mb low
associated with the tropical wave along 33W, and from this low to
08N41W where it transitions to the ITCZ. The ITCZ then continues
to 08N50W and to 08N59W. Aside from the convection described
above associated with the two potential tropical cyclone systems,
only scattered moderate convection is seen within 60 nm of the
ITCZ between 47W and 53W. Similar convection is south of the ITCZ
within 30 nm of 07N41W.

...DISCUSSION...

GULF OF MEXICO...

Upper-level cyclonic flow is located over eastern Louisiana and
Mississippi while upper-level anticyclonic flow is located over
the west-central Gulf of Mexico. A moist and unstable atmosphere
along with plenty available instability is allowing for scattered
showers and isolated thunderstorms to be over much of the NW Gulf
and far western gulf waters. Scattered moderate convection that
moved offshore the west coast of Florida last night is seen
over the eastern gulf waters from 25N to 30N between 83W and 85W,
and over the far southeastern gulf waters just west of the lower
Florida Keys to near 84W and from 23N to 25N. Isolated showers
and thunderstorms are elsewhere across the Gulf. Expect for
shower and thunderstorm activity to remain over these same gulf
waters through at least tonight.

Otherwise, weak ridging from the Carolinas to the Texas coast
will shift northward through Sat, supporting gentle to moderate
easterly winds and modest seas into early next week. The exception
will be fresh winds pulsing off west of the Yucatan peninsula,
mainly during the late evenings through the next few days.

CARIBBEAN SEA...

Please see Tropical Waves section above for details regarding
a tropical wave along 80W/81W.

An upper-level trough axis stretches from central Cuba to 18N83W
and to over eastern Honduras. Associated cyclonic flow covers the
western Caribbean Sea west of a line from Hispaniola to Panama.
Upper-level anticyclonic flow covers the eastern Caribbean as the
culprit anticyclone remains anchored near 17N61W. Aside from
convection related to the tropical wave, isolated showers and
thunderstorms are elsewhere west of 71W.

A relatively weak surface ridge in the western Atlantic Ocean
will maintain moderate to fresh trade winds in most of the region
into Sun. Building high pressure over the eastern Gulf of
Mexico will allow fresh to strong E to SE winds and building
seas over portions of the NW Caribbean late Sun and Mon.

ATLANTIC OCEAN...

Please read the Special Features section above for details about
Hurricane Florence. Two areas of tropical development interest
pertains to a broad area of low pressure in the eastern Atlantic
near 14N33W, with a high chance of development and a vigorous
tropical wave and low pressure system very near the coast of
Africa also with a high chance of tropical development.

A large upper-level low centered over the NW Bahamas extends a
trough southwestward across central Cuba. The low continues
progressing in a westward motion. Its associated upper-level
cyclonic flow covers the Atlantic west of 66W, and northward to
about 35N. A westward moving surface trough is analyzed from
31N75W to the NW Bahamas and to just north of the coast of Cuba
near 23N79W. Another surface trough is analyzed from near 32N66W
to 28N67W. Plenty of available atmospheric instability for these
features to work on has resulted in scattered showers and
thunderstorms over the waters north of 25N between 67W and 78W.
Isolated showers and thunderstorms are elsewhere west of 65W,
and also north of 28N between 50W and 65W.

A weak pressure pattern will maintain gentle to moderate easterly
winds across the western Atlantic area into early next week.
Tropical Storm Florence is forecast by the latest NHC advisory to
move across the northeastern NHC/TAFB offshore waters zones Mon
through Tue of next week. Easterly swell, in advance of Florence,
are forecast to propagate through the open waters east of the
Bahamas beginning this weekend. For additional information please
visit http://www.hurricanes.gov/marine

$$
Aguirre
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