[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 291045
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Wed Sep 29 2021

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 31N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 1200 UTC surface analysis and satellite imagery through
1030 UTC.

...SPECIAL FEATURES...

Hurricane Sam was centered near 18.9N 56.2W at 29/0900 UTC or 400
nm E of the Northern Leeward Islands moving NW at 8 kt. Estimated
minimum central pressure is 950 mb. Maximum sustained wind speed
is 115 kt with gusts to 140 kt. Maximum significant wave heights
are 35 ft near the center, while the 12 ft seas extend out as far
as 180 n mi from the center. Latest satellite imagery shows a
cloud-filled eye about 15 nm in diameter. Numerous strong
convection is within 90 nm of the center in the E semicircle and
within 50 nm of the center in the W semicircle. Scattered
moderate isolated strong convection is elsewhere within 200 nm N
semicircle, 120 nm SE quadrant and 90 nm SW quadrant. Sam will
continue moving northwest with an increase in forward speed during
the next couple of days. A turn toward the north is forecast by
Friday. On the forecast track, Sam will pass well to the east and
northeast of the northern Leeward Islands through tonight. Some
fluctuations in intensity are expected during the next couple of
days, but Sam is forecast to remain a major hurricane through late
this week. Swells generated by Sam will impact the Lesser
Antilles during the next several days. Swells are expected to
reach Bermuda and the Bahamas in a day or two, and then spread to
the United States east coast by this weekend. These swells could
cause life-threatening surf and rip current conditions. Please read the latest
High Seas Forecast issued by the National Hurricane Center at
website https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the
latest NHC Forecast/Advisory and Public Advisory at
www.hurricanes.gov for more details.

East Atlantic Gale Warning: A 1007 mb low pressure near 07N23W
is along a tropical wave that extends along 23W from 02N-15N,
moving W at 10-15 kt. Numerous strong convection from 06N-11N
between 21W-26W is showing signs of organization. Scattered
moderate convection is elsewhere from 04N-12N between 20W-30W.
Environmental conditions are conducive for additional development,
and a tropical depression or tropical storm is likely to form later
today or tonight while the disturbance moves west-northwestward at
10 to 15 mph over the eastern tropical Atlantic. This system has a
high chance of formation in the next 48hours. Please read the
latest High Seas Forecast issued by Meteo- France at website
http://weather.gmdss.org/II.html regarding the gale warning for
this system.

A 1009 mb low pressure is near 07N32W. Scattered moderate
convection from 02N-07N between 30W-39W remains disorganized.
Although environmental conditions are generally conducive for
development during the next day or so, interaction of this system
with the low pressure area located to its east is likely to hinder
development after that time. The system is forecast to drift
west-northwestward over the next few days. This system has a
medium chance of tropical cyclone formation.

Please refer to the latest NHC Tropical Weather Outlook at
www.hurricanes.gov for more details on the two tropical
disturbances.

...TROPICAL WAVES...

A central Atlantic tropical wave is along 40W from 17N southward, moving
W at 15 kt. Scattered moderate convection is within 100 nm east
of the wave from 04N to 11N.

A western Caribbean tropical wave is along 81W south of 17N to
across Panama. It is moving W near 10 kt. Scattered moderat convection
is noted from 10N to 12N between 79W and 83W. This activity is
being further enhanced by the eastern segment of the east Pacific
monsoon trough.

...MONSOON TROUGH/ITCZ...

A monsoon trough enters the Atlantic through the coast of
Mauritania near 17N16W to the aforementioned 1007 mb low near
07N23W to the aforementioned 1009 mb low near 07N32W to 05N39W.
The ITCZ extends from 04N42W to the coast of French Guiana near
04N52W. Aside from convection mentioned in the sections above,
scattered moderate convection is noted along the ITCZ from 04N to
08N between 41W and 52W.

GULF OF MEXICO...

Scattered to numerous moderate convection continues over much of
the northwest Gulf of Mexico north of 26N and west of 87W. This
is occurring in an area where strong upper-level diffluence is co-
located with mid-level SW winds, transporting ample moisture
northward from the tropics. Expect more scattered showers and
tstorms over the northwest and north-central Gulf of Mexico today.
A 1016 mb high pressure is centered near 29N84W in the northeast
Gulf and the ridge extending acorss most of the Gulf.
Thunderstorms are also occurring over the southern Bay of
Campeche. Overnight ASCAT pass shows fresh SE to S winds near the
coast of south Texas and northeast Mexico. Fresh E winds are
noted just off the coast of the NW Yucatan Peninsula. Light to
gentle winds are seen in the NE Gulf near the high pressure.
Moderate wind speeds are elsewhere. Seas of 2 to 4 ft cover most
of the Gulf, except 1 to 2 ft in the NE Gulf.

For the forecast, weak high pressure will stay in place over Gulf
through Fri. Moderate to locally fresh southerly winds are
expected in the western Gulf through Thu with gentle winds in
the eastern Gulf. A weak cold front will press southward over the
eastern Gulf on Fri and weaken by Sat. Stronger higher pressure
will build across the region through Sat. Moderate to fresh winds
are expected to prevail in the eastern Gulf with gentle to
moderate winds in the western Gulf through the weekend.

CARIBBEAN SEA...

Isolated thunderstorms continue south of the Greater Antilles and
to the west of the Lesser Antilles. Thunderstorms are also noted
north of Colombia between 73W and 75W. Overnight ASCAT pass
showed gentle trade winds across most of the basin, except for
moderate in the south- central Caribbean. Seas are averaging 2 to
3 ft across the basin, except 3 to 4 ft over the south-central and
SE Caribbean.

For the forecast, gentle trades will prevail over the Caribbean
through Fri. Swells generated by Sam are forecast to continue off
the Leeward Islands through Thu and will begin to impact the Mona
and Anegada Passages later today through Fri. Winds are expected
to increase moderate to fresh across the basin by the weekend.

ATLANTIC OCEAN...

Please read the Special Features section above for details on
Hurricane Sam and on two tropical disturbances in the eastern
part of the Atlantic Basin.

The Cumbre Vieja volcano on the island of La Palma in the Canary
Islands near 28.6N 17.8W has been erupting since September 19th.
Medium concentration of volcanic ash is expected near, and up to
40 nm southeast of the volcano. Marine and aviation interests
should monitor this ongoing situation by reading Volcanic Ash
Advisory issued by Meteo-France at
http://vaac.meteo.fr/volcanoes/la-palma/ for details. The next
advisory will be issued no later than 29/0900 UTC.

Over the west Atlantic, a surface trough extends from 28N60W to
23N70W. Scattered showers and tstorms are noted along and N of
the trough from 25N-27N between 66W-69W. A 1017 mb high pressure
is near 31N78W. Gentle winds cover most of the area west of 62W
except for moderate to fresh E winds in the Florida Straits.
Seas are 2 to 4 ft west of 70W, but higher farther east due to
swell from Hurricane Sam. Over the eastern Atlantic, a surface
trough extends from 22N39W to 30N37W. Scattered moderate showers
and tstorms are along the portion of the trough north of 25N.
The Tuesday evening ASCAT pass showed strong to near gale force
NE winds off the coasts of Morocco and Western Sahara, extending
SW through the Canary Islands, and including most of the area
from 21N-29N, east of 30W. Seas are likely 9 to 11 ft within
these areas.

For the forecast, Hurricane Sam will move to near 22N60W Thu
morning, 26N62W Fri morning, 29N62W Fri evening, and near 35N58W
Sat evening. In addition to hurricane conditions northeast of the
Leeward Islands through tonight, expect rough seas in the form
of swell from Sam east of 70W Thu and Fri. Farther west, a weak
pressure pattern will maintain light to gentle breezes and
slight seas through Thu. A cold front will move from the
Carolinas to the central Bahamas Fri and Sat, then stall and
dissipate through late Sun.

$$
AReinhart

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