[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 031544
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1144 AM EDT Thu Sep 3 2020

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
1715 UTC.

...SPECIAL FEATURES...

Tropical Storm Nana is centered near 16.4N 90.3W at 03/1500 UTC
or 110 nm N of Guatemala City Guatemala moving W at 13 kt.
Estimated minimum central pressure is 1004 mb. Maximum sustained
wind speed is 40 kt with gusts to 50 kt. On the forecast track,
the center of Nana will move over northern Guatemala and
southeastern Mexico today and tonight, then move over the Gulf of
Tehuantepec on Friday. Continued rapid weakening is forecast, and
Nana will likely become a remnant low on Friday. Nana is forecast
to produce rainfall amounts of 3 to 6 inches, isolated totals of 8
inches over central and western Guatemala and the Mexican state of
Chiapas. These rainfall amounts may produce life threatening
flash floods and mudslides.  Please consult products from your
local weather office. Please read the latest NHC Public Advisory
at https://www.nhc.noaa.gov/text/MIATCPAT1.shtml and Forecast/
Advisory at https://www.nhc.noaa.gov/text/MIATCMAT1.shtml for more
details.

Tropical Depression Omar is centered near 35.9N 61.1W at 03/1500
UTC or 290 nm NE of Bermuda moving E at 11 kt. Estimated minimum
central pressure is 1005 mb. Maximum sustained wind speed is 30
kt with gusts to 40 kt.

The center of Omar is
currently exposed due to fairly strong WNW shear impacting the
system. But a large area of strong thunderstorms is observed just
to the east of the center. Omar is expected to gradually weaken
over the next couple of days as it moves northeast. Please read
the latest NHC Public Advisory at
https://www.nhc.noaa.gov/text/MIATCPAT5.shtml and Forecast/
Advisory at https://www.nhc.noaa.gov/text/MIATCMAT5.shtml for more
details.

...TROPICAL WAVES...

A tropical wave that has emerged off the west coast of Africa is
along 18N, from 18N southward. A 1008 mb low pressure is analyzed
along the wave axis near 14N. The low pressure is well defined on
visible satellite imagery, and scatterometer data show fresh SW
winds on the SE quadrant of the low center. This system is
producing a large area of scattered moderate convection from 10N-
15N between 16W-22W. This wave is merging with another disturbance
located a couple of hundred miles south of the Cabo Verde Islands.
Development of this system is likely to be slow during the next
couple of days while it moves west-northwestward at about 15 mph,
and a tropical depression is more likely to form early next week
over the central tropical Atlantic where environmental conditions
are forecast to be more favorable for development. The latest
Tropical Weather Outlook states that this system has a high chance
of tropical cyclone formation through 5 days. Refer to the latest
Tropical Weather Outlook at www.hurricanes.gov for more details.

A tropical wave is along 25W, from 18N southward, moving westward
10 to 15 knots. A 1008 mb low pressure is along the wave axis near
12N. Scattered moderate to isolated strong convection is observed
mainly to the west of the low center from 11N-13N between 22W-
27W. There system has a low chance of tropical cyclone formation
within the next 48 hours, but a high chance that a tropical
depression will form through the next five days. Refer to the latest
Tropical Weather Outlook at www.hurricanes.gov for more details.

Another tropical wave is analyzed along 43W/44W S of 18N based on
Tropical Wave Diagnostic. A swirl of low clouds is noted near the
northern end of the wave axis.

A tropical wave is along 57W from 19N southward. Visible satellite
imagery shows a well defined inverted-V pattern associated with
the wave. Some shower activity is noted near the wave axis but
mainly from 12N-16N. Moisture related to this wave will spread
over the Lesser Antilles tonight into Fri.

A Caribbean tropical wave is along 61W from 20N southward, moving
W 10 to 15 knots. Scattered moderate convection is active from 11N
to 13N between 62W and 65W.

A Caribbean Sea tropical wave is along 75W from 18N southward,
moving W 10 to 15 knots. Scattered moderate to isolated strong
convection is observed from 13N to 17N between 75W and 80W.

...MONSOON TROUGH/ITCZ...

The monsoon trough passes through the southern coastal sections
of Mauritania, to 13N25W, to 1008 mb low pressure near 13N36W to
13N55W. IN addition to the convection described in the Tropical
Waves section, scattered moderate convection is evident south of
the monsoon trough from 09N to 13N between 15W and 20W, and from
06N to 10N between 25W and 32W. Scattered moderate convection is
also noted within 120 nm east of the low pressure near 13N36W.

GULF OF MEXICO...

A surface ridge extends westward across the northern Gulf coast from
1017 mb high pressure centered off Apalachicola Florida. E winds
to 20 kt are active over the south central Gulf, between the high
pressure and lower pressure farther south in the northwest
Caribbean, on the northern periphery of Nana. Fresh NE winds are
also noted off the west coast of the Yucatan peninsula, due to a
short duration local effect common this time of the morning. Recent
buoy observations along with a scatterometer pass from 04 UTC
indicated moderate to occasionally fresh southerly flow elsewhere
over the western and southern Gulf, with light to gentle breezes
under the high pressure over the northeast Gulf. Buoy observations
and altimeter data showed seas of 4 to 6 ft in south central
Gulf, 1 to 3 ft in the northeast Gulf, and 3 to 5 ft elsewhere. A
few showers are active over the south central Gulf as well this
morning related in part to low level convergence in the easterly
flow, but also due to divergent flow aloft over the area
associated with a small upper low off Louisiana.

The high pressure over the northeastern Gulf will dissipate
through Fri ahead of a weak front moving into the northern Gulf
Sat. The front will stall over the northern Gulf Sun, then slowly
dissipate through early next week. Looking further ahead, another
stronger front may enter the northwest Gulf by mid week.

CARIBBEAN SEA...

Please see the Special Features section above for information on
T.S. Nana.

A moist pattern prevails across the Caribbean in the wake of Nana.
Satellite-derived precipitable water values show very high deep
layer moisture over most of the basin. Clusters of showers and
thunderstorms are observed in a large swath from the southern
Windward Islands to almost northeast Nicaragua. under diffluent
flow aloft. Showers and thunderstorms are also active west of
Grand Cayman and south of western Cuba, on the east side of an
upper trough. The track of Nana has temporarily interrupted the
usual trade wind patterns in the Caribbean. This is leaving the
normally rainy southwest Caribbean mostly rain free. Fresh trade
winds and 4 to 6 ft seas are possible off southern Hispaniola,
but elsewhere gentle to moderate winds are noted, with light and
variable breezes in the southwest Caribbean.

E swell in the northwest Caribbean will subside through the
morning. The Caribbean will gradually revert back to its normal
pattern over the next several days with moderate to fresh trade
winds mainly over the central part of the basin.

ATLANTIC OCEAN...

A weak surface ridge extends east to west across the waters north
of 27N. This is supporting moderate to fresh trade winds south of
22N, and lighter winds farther north into the ridge. Seas are
generally 4 to 6 ft in open waters outside of the Bahamas. An
upper level low centered north of the Leeward Islands is
supporting a cluster of showers and thunderstorms about 150 nm
northeast of the Virgin Islands. Subsident NE flow aloft between
the upper low and and an upper anticyclone centered off the
Carolinas is inhibiting significant convection elsewhere in the
western Atlantic, west of 65W. The ridge will dissipate by Sun
ahead of a weak frontal boundary entering the area from the north,
but otherwise little change is expected into early next week W of
65W.

Farther east, fresh SW winds and 6 to 8 ft seas are active south
of the monsoon trough mainly east of 35W. As stated in the
tropical waves section, this area may become active over the next
several days, and there is a high chance a tropical depression
will form in the eastern or central tropical Atlantic by early
next week.

$$
GR
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