[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 181711
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
111 PM EDT Tue Aug 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 1200 UTC surface analysis and satellite imagery through
1700 UTC.

...SPECIAL FEATURES...

A broad 1009 mb low near 12N38W is moving west at 15-20 kt. This
location is about 800 nm WSW of the Cabo Verde Islands. The system
is producing numerous moderate to scattered strong convection from
10N to 14N between 33W and 42W. Environmental conditions are
conducive for development, and there is a high chance a tropical
depression will form within the next day or two. This system may
approach the vicinity of the Leeward Islands by Friday or early
Saturday. Please refer to the latest NHC Tropical Weather Outlook
at www.hurricanes.gov for more details.

...TROPICAL WAVES...

A tropical wave has its axis along 31W from 02N to 21N, moving
westward at about 15 kt. This wave is moving through a moist
surrounding environment. Numerous moderate to scattered strong
convection is noted from 10N to 14N between 30W and 33W. Over the
next day or two, this wave is forecast to approach the low
pressure mentioned above in the Special Features section and its
associated tropical wave.

A tropical wave is analyzed along 46W from 05N to 23N, moving
west at 10 to 15 kt. This tropical wave is being enhanced by an
upper low to its northwest, near 23N52W, and the relatively sharp
axis of the tropical wave shows up fairly well in the lower to
mid levels of the atmosphere in satellite derived wind flow data.
No significant convection is observed in the vicinity of the wave
axis.

A strong tropical wave is analyzed in the eastern Caribbean
along 65W south of 21N, moving west at 20 kt. Numerous moderate
to scattered strong convection is seen between 13N and 15N between
63W and 67W. Rich deep layer moisture accompanies the tropical
wave, and heavy rainfall has been reported over the Windward
Islands over the past 24 hours as the tropical wave moved through
the region. Trinidad reported a 24 hour total over three inches
of rainfall by earlier this morning. A recent scatterometer pass
indicated a broad area of fresh NE winds over the northeast
Caribbean, mainly south of Puerto Rico. Slightly stronger winds
are possible farther south, outside of where the scatterometer
sampled. The locally heavy rainfall and gusty winds over portions
of the Windward and southern Leeward Islands is gradually
subsiding as the tropical wave and main area of moistures shifts
westward. This wave is expected to continue moving quickly west
over the eastern and central Caribbean Sea during the next couple
of days, which is likely to limit significant development. After
that time, the system is forecast to move more slowly westward and
into the northwest Caribbean, where upper- level winds could
become more conducive for the development of a tropical depression
during the latter part of this week. The chance of development
within the next 48 hours is low, with a moderate chance later in
the week.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from the coast of Mauritania,
Africa near 18N19W southwestward to 11N30W to the developing low
pressure near 12N38W, then on to 10N45W. The intertropical
convergence zone continues toward 10N60W. Aside from the
convection related to the tropical waves and low pressure
described above, scattered moderate convection is observed from
05N to 07N between 38W and 45W.

GULF OF MEXICO...

A weak, nearly stationary trough reaches from near Panama City
Florida to 28N90W, to near Galveston, Texas. The pressure pattern
remains fairly weak across the basin, and buoys are showing mostly
light to gentle breezes. Seas are 1 to 3 ft in most areas. A few
showers are noted within 90 nm south of the trough axis over the
central and northwest Gulf, but otherwise no significant showers
or thunderstorms are noted.

For the forecast, the weak pressure pattern will continue across
the Gulf through Wed night before high pressure over the central
Atlantic builds modestly across Florida and into the eastern basin
Thu through Fri. Looking ahead, fresh to strong winds are
possible Sun over the south central Gulf with and ahead of a
tropical wave and potential low pressure approaching the region
from the northwest Caribbean and Great Bahama Bank.

CARIBBEAN SEA...

See the Tropical Waves section above for details on the strong
tropical wave in the eastern Caribbean.

Elsewhere across the basin, scattered moderate showers and
thunderstorms are ongoing over the southwest Caribbean, along the
coasts of Costa Rica and western Panama, north of the monsoon
trough. A few showers and thunderstorms active off Belize ealier
this morning have diminished. Seas are estimated to be 5 to 8 ft
in the eastern Caribbean due to the fresh to strong winds near the
tropical wave. Seas are 3 to 5 ft with moderate to fresh trades
in the south central Caribbean, and 1 to 3 ft with light to gentle
breezes over the northwest Caribbean.

For the forecast, in addition to the impacts of the tropical wave
currently over the eastern Caribbean as discussed in the Special
Features section, low pressure associated with another
tropical wave is expected to approach the Atlantic waters off the
Leeward Islands Fri or Sat. This may bring gusty winds and a few
showers to the far northeast Caribbean then.

ATLANTIC OCEAN...

See Special Features section above for information on the low
pressure in the central tropical Atlantic.

A weak cold front extends to 30N78W from 1010 mb low pressure
north of the area, about 210 nm east of Cape Hatteras. A few
showers are noted along this weak boundary, but they are
diminishing. A trough lingers off the central Bahamas, and a small
cluster of showers and thunderstorms is noted within 30 nm of
24N68W. Another cluster is evident north of 28N between 60W and
65W. The subtropical ridge is oriented east to west along roughly
28N east of 70W, from 1020 mb high pressure centered near 28N35W.
This pattern is allowing generally light winds and moderate seas
over the area west of 60W. Moderate to occasionally fresh trades
are evident south of this ridge from 15N to 20N over the central
Atlantic, with 4 to 6 ft seas. Fresh to strong NE winds are noted
off the coasts of Morocco and Western Sahara, where seas are
estimated to be 6 to 9 ft.


For the forecast west of 60W, the high pressure centered over the
central Atlantic will continue to dominate this week, bringing
gentle to moderate mainly southerly winds north of 23N. An
elongated area of low pressure associated with the tropical wave
over the central tropical Atlantic is forecast to move W or WNW
this week, and through an environment that is favorable for
tropical development. A tropical depression is likely to form in
the next day or two. This system is forecast to be northeast of
the Leeward Islands Fri or Sat.

$$
Christensen
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