[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 180906
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Wed Nov 18 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 0600 UTC surface analysis and satellite imagery through
0900 UTC.

...SPECIAL FEATURES...

Tropical Depression Iota is centered near 13.7N 88.3W at 18/0900
UTC or 20 nm NW of El Papalon, El Salvador moving WSW at 11 kt.
Estimated minimum central pressure is 1007 mb. Maximum sustained
wind speed is 30 kt with gusts to 40 kt. Additional weakening is
forecast, and Iota is expected to degenerate into a post-tropical
remnant low pressure system later today. Most of the deep
convection associated with Iota has dissipated, however a few
disjointed bands of scattered moderate and isolated strong
convection are noted across portions of the western Caribbean.
Life-threatening flash flooding and river flooding is expected
through Thursday across portions of Central America due to heavy
rainfall from Iota. Flooding and mudslides across portions of
Honduras, Nicaragua and Guatemala could be exacerbated by saturated
soils in place, resulting in significant to potentially catastrophic
impacts. 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.

Gulf of Mexico Gale Warning: Strong autumn high pressure will
continue to build southward across the Gulf of Mexico behind a
cold front that extends from the Straits of Florida to the
N-central Yucatan Peninsula. The high pressure will continue to
create a very tight gradient between it and the front leading to
strong northeast winds, with frequent gusts to gale force over the
southeastern half of the Gulf waters, including the Straits of
Florida and the waters adjacent to the Yucatan Channel through
early Thursday, 19/1200 UTC. Expect building seas of 10-16 ft
across this area. Very hazardous conditions can be expected
between the wind waves against the flow of the Gulf stream through
the Straits of Florida, and due to a SE swell generated by Iota
which is propagating through the Yucatan Channel. Please read the
latest NWS High Seas Forecast issued by the National Hurricane
Center at website https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml
for more details.

Caribbean Gale Warning: The same conditions that are occurring in
the southeastern half of the Gulf of Mexico behind a cold front
approaching the basin will spread into the far northwestern
Caribbean with gusts to gale force behind the front and N of 20N
from later this morning, 18/1200 UTC through early Thursday,
19/1200 UTC. The cold front is forecast to stall from eastern Cuba
to the Gulf of Honduras early Thu. Large and hazardous seas will
build to 8 to 13 ft through the Gulf of Honduras and the Yucatan
Channel as fresh northerly wind waves behind the front mix with
E-SE swell generated by Iota. The highest seas are expected in
the Yucatan Channel. Please read the latest NWS High Seas Forecast
issued by the National Hurricane Center at website
https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml for more details.

Atlantic Gale Warning: The pressure gradient which will lead to
frequent gusts to gale force over the southeastern Gulf of Mexico
and far northwestern Caribbean Sea will also bring frequent gusts
to the western Atlantic off the coast of South Florida and the
Bahamas behind the cold front which currently extends from 31N64W
to near 23N80W across the basin. These gusts will begin this
evening, 19/0000 UTC through Thursday evening, 20/0000 UTC
offshore the Bahamas from 22N to 27N and W of 65W. Expect seas to
build to 8-14 ft with the highest first in the gulf stream, then
to NE of the Bahamas by Thursday night. Please read the latest NWS
High Seas Forecast issued by the National Hurricane Center at
website https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml for more
details.

...TROPICAL WAVES...

The axis of a low amplitude tropical wave is near 39W/40W from
the equator to 12N, moving westward at 15-20 kt. Scattered
moderate convection is noted from 07N-10N between 37W-43W.

The axis of a tropical wave is near 60W/61W from 21N southward
across the Lesser Antilles to near the border of Guyana and
Venezuela, moving westward around 10 kt. Scattered moderate
convection is noted from 12N-14N between 60W-65W, and from 20N-24N
between 60W-63W.

The axis of a tropical wave is near 72W/73W from the western
Dominican Republic southward to NE Colombia just W of the Gulf of
Venezuela, moving westward at around 10 kt. Scattered moderate and
isolated strong convection is noted E of the tropical wave axis to
68W with very heavy rainfall occurring along the coast of
Venezuela and the ABC Islands.

...MONSOON TROUGH/ITCZ

The monsoon trough axis extends from the coast of Africa near the
Guinea/Sierra Leone border to 07N17W. The ITCZ axis continues
from 0717W to 05N30W to 05N40W then resumes W of a tropical wave
near 04N41W to the coast of Brazil near to 06N35W. The ITCZ
continues west of a tropical wave near 06N38W to the coast of
Brazil near 03N51W. Scattered moderate and isolated strong
convection is noted from 04N-07N betwen 10W-13W. Scattered
moderate convection is noted from 02N-07N between 22W-30W.
Scattered moderate and isolated strong convection is noted from
05N-09N between 30W-37W, and from 02N-07N between 44W-52W with a
surface trough noted from 09N45W to 05N48W.

GULF OF MEXICO...

See Special Feature section above for details on a Gale Warning
in effect over the southeastern half of the Gulf of Mexico.

The cold front extends westward from the Straits of Florida near
23N80W to the N-central Yucatan Peninsula. Showers are noted
along the front. A trough extends in the western Bay of Campeche
from 22N95W to 18N94W.

The cold front will move SE of the basin later this morning.
Conditions across the basin will improve by the end of the week
into the weekend as the high pressure behind the front weakens and
slides eastward to the Carolinas. Expect fresh to locally strong
NE-E flow E of 87W, and moderate to fresh E-SE flow W of 87W by
early Sat with subsiding seas, then moderate E-SE winds E of 87W
and gentle to moderate NE-E winds W of 87W by Sun evening.

CARIBBEAN SEA...

Please see the Special Features section for information on
Tropical Depression Iota and on a Gale Warning in effect for the
northwestern Caribbean north of 20N.

A cold front is just NW of the basin and will move into the far NW
Caribbean later this morning, as is described above. Ahead of this
front, fresh to strong NE winds are already occurring across the
NW Caribbean due to a tight pressure gradient between Tropical
Depression Iota and building high pressure N of the area. Mainly
moderate trades prevail elsewhere, locally fresh in the eastern
Gulf. Seas are 8-13 ft in the NW Caribbean in mixed NE wind waves
and remnant E-SE swell generated by Iota. Seas of 3-6 ft prevail
elsewhere across the basin.

The cold front will stall by early Thursday and will gradually
wash out Friday through Saturday, and the pressure gradient N of
the remnant boundary will weaken. Thus trades will weaken across
the basin this weekend with marine conditions improving.

A 1008 mb low pressure area is noted in the SW Caribbean Sea near
11N83W. Environmental conditions are expected to be only
marginally conducive for slow development over the next several
days while the system moves slowly west-southwestward or westward
across the southwestern Caribbean Sea. Regardless of tropical
cyclone formation, areas of heavy rain are possible during the
next several days from Nicaragua southward across Central America
and into Colombia. These rains could cause new flooding concerns,
especially across previously inundated areas. Please read the
latest Tropical Weather Outlook issued by the National Hurricane
Center at website https://www.nhc.noaa.gov/text/MIATWOAT.shtml
for more details.

ATLANTIC OCEAN...

See the Special Features section for details on a Gale Warning in
effect over the SW N Atlantic.

SE of the cold front discussed above, a trough is analyzed from
28N63W to 22N66W. Scattered moderate convection is noted within 45
nm either side of the trough N of 25N. Mainly moderate NE-E winds
prevail W of 65W along with seas of 4-6 ft. Another cold front is
analyzed in the eastern and central Atlantic, extending from
32N20W to 27N40W. Scattered showers are noted near the front.
Associated seas of 7-10 ft have propagated S of the front reaching
to 20N. A surface trough is analyzed in the tropical central
Atlantic from 20N48W to 24N49W with isolated showers near the
trough. Moderate to fresh easterly winds are noted across the
waters E of 60W, with gentle to moderate winds between 60W-65W.
Seas are 5-8 ft across the remainder of the basin in mixed swell.

The cold front in the SW N Atlantic will stall from near 26N65W to
near the Turks and Caicos Thu night, gradually weakening and then
drifting back NW as a remnant warm front through the end of the
week before dissipating by early Sat. A non-tropical area of low
pressure could form between the Bahamas and Bermuda by early next
week along the remnants of the front. The system could gradually
develop subtropical characteristics through the middle of next
week while it moves northeastward. Please read the latest Tropical
Weather Outlook issued by the National Hurricane Center at
website https://www.nhc.noaa.gov/text/MIATWOAT.shtml for more
details.

$$
Lewitsky
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