[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 170003
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
803 PM EDT Sun Jul 16 2017

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 1800 UTC surface analysis and satellite imagery through
2345 UTC.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave was introduced to the
surface analysis this afternoon roughly along a position from
16N27W to 09N28W based on low to mid-level satellite winds,
the Total Precipitable Water (TPW) imagery loop from a 24 hour
period, and on mid-level potential vorticity and wind model
guidance. The wave is moving westward about 10-15 kt, and is
mostly embedded in deep tropical moisture that is associated with
the monsoon trough segment that extends from West Africa to the
the far eastern Atlantic. The latest TPW loop animation and
METEOSAT-9 imagery both depict the moisture around this wave.
Deep convection associated with the wave consists of the
scattered moderate type intensity within 150 nm west of the wave
along and near the monsoon trough from 09N to 11N. The latest
data from the METEOSAT imagery does show extensive Saharan dust
covering the eastern Atlantic section from just over the far
northern part of the wave, and also well to the north and
northeast of the wave.

A central Atlantic tropical wave has its axis extending from
near 15N49W to 11N50W and to 04N50.5W, moving westward near
7 kt. This wave marks the leading edge of a broad area of low
pressure that encompasses the monsoon trough and covers the
area well to the east of the wave to 40W and from 07N to 14N.
At 1800 UTC, a 1011 mb low is analyzed near 10.5N46W moving
generally westward near 13 kt. The CIRA moisture guidance
depicts very a very deep moisture column through the broad
area of low pressure and tropical wave. The latest satellite
imagery shows scattered moderate to isolated strong convection
between 60 and 120 nm of the low in the northwest quadrant.
Scattered moderate convection is within 60 nm west of the wave
along the monsoon trough from 09N to 11N. Both the TPW imagery
loop and the latest METEOSAT imagery confirm the presence of very
dry and stable air in the Saharan Air Layer north of 15N and east
of 50W. The low pressure may develop some over the next 48 hours
as it continues to the west.

A western Caribbean tropical wave has its axis extending from
near 18N79.5W to 13N80W, to central Panama at 09N80W and
southward to the eastern Pacific near 07N80W. The wave
has moved 20 kt during the past 24 hours, but appears to have
slowed down some this afternoon and evening to an estimated speed
of about 16 kt. Latest visible satellite imagery shows a broad
field of low clouds moving in northeast to southwest fashion
within 180 nm either side of the wave axis. Deep moisture and
convection is being enhanced along and near the wave south of
16N due to the nearby proximity of an upper level low situated
at 11N81W. The observed convection is seen in clusters of
the scattered moderate type intensity from 13N to 15N between
78W-83W and within 60 nm of the axis from 10N-13N. This wave
will move across the western Caribbean through early Monday
afternoon before moving inland central America late Monday
afternoon or evening.

The earlier far western Caribbean tropical wave has moved inland
central America and the Yucatan Peninsula to along 90W. It extends
southward to the eastern Pacific to near 07N90W, and is moving
westward near 15 kt. The combination of daytime heating and energy
from this wave has induced clusters of scattered moderate
convection over much of the Yucatan Peninsula, Belize and
Honduras.

...ITCZ/MONSOON TROUGH...

The Monsoon Trough axis extends from 14N17W to 11N25W to 10N32W
to the 1011 mb tropical low at 10.5N46W and to just east of the
tropical wave along 50W/51W. The ITCZ axis extends from just west
of the same wave to 07N58W. Aside from the convection related to
both Atlantic tropical waves and the tropical low as discussed
above, scattered moderate to strong convection is seen within '
120 nm north and 60 nm south of the monsoon trough axis between
35W-39W. Scattered moderate isolated strong convection is
within 120 nm north of the ITCZ axis between 52W-56W and within
60 nm north of the same axis between 56W-58W.

Scattered moderate isolated strong convection is south of the
monsoon trough from 03N to 08N between 40W-45W.

...DISCUSSION...

GULF OF MEXICO...

An upper level low moving westward is over the far SW Gulf near
21N96W, with a cyclonic shear axis extending from the low
northeast to 25N90W and to just south of the base of an upper
trough near 29N84W. Upper level northeast flow is present to the
northwest of the shear axis and low. A small upper level low is
noted over S Florida. At the surface, a trough is analyzed over
the far NW Gulf from just south of southwestern Louisiana to just
northeast of Brownsville. The analysis revealed a very weak
pressure gradient over the area that supports generally light to
gentle winds throughout. Latest mosaic NW Doppler radar display
along with satellite imagery shows scattered showers and isolated
thunderstorms east of 91W, and also north of 25N west of 91W. The
majority of this activity is waning. Scattered showers and
thunderstorms are just offshore NW Cuba and the northern Yucatan
Peninsula. Conditions across most of the Gulf are expected to
remain very moist and unstable through early next week. A surface
trough is approaching S Florida and the Straits of Florida. Expect
showers and thunderstorms to remain quite active over the Straits
and far southeastern Gulf into Monday.

CARIBBEAN SEA...

A tropical wave is along a position from 18N79.5W to 13N80W. See
the section above for a discussion on this feature. Aside from
the convection related to the aforementioned tropical wave,
scattered moderate convection is over the northwest portion of
Jamaica, and being enhanced by a small upper level low noted on
water vapor imagery near 19N80W. The low is forecast to move off
to the northwest through early next week. A deep pool of moisture
resides across much of the southwestern portion of the sea.
Resultant convective activity is described above in relation to
the tropical wave. The water vapor imagery shows very dry air
aloft across the eastern portion of the sea. Only isolated showers
moving from east to west in low cloud lines are noted there. A
tropical wave with associated low pressure is forecast to move
across the Lesser Antilles and into the eastern Caribbean Sea on
Tuesday accompanied by increasing winds and seas.

...HISPANIOLA...

Scattered moderate to strong convection is presently over much
of Haiti and the central and western section of the Dominican
Republic. This activity will gradually weaken tonight. The
presence of a very moist air mass in place along with the
typical local island effects with daytime heating will allow
for more of the same type of activity to develop on Monday
afternoon and last into the evening hours.

ATLANTIC OCEAN...

Tropical waves are identified over the far eastern and central
Atlantic. See the section above for discussions on these features.
A large upper level low lifting northward is located on water
vapor imagery to be near 30N70W, with a trough stretching
southwestward to 26N70W to the southeastern Bahamas and to the
eastern tip of Cuba. Another large upper level low gradually
moving westward is over the north-central portion of the area at
29N49W, with a trough extending southwestward to 19N54W and
southward to an elongated upper low at 15N55W. A small upper low
is over the waters between the central Bahamas and central Cuba.
Broad upper troughing is just northwest of the discussion area
approaching the eastern United States. At the surface, a 1029 mb
high is analyzed at 35W36W moving westward at 15 kt. A ridge
extends from the high west-southwestward to 32N60W and to just
east of NE Florida. A surface trough associated with an upper low
over S Florida is along a position from 27N79W to just north of
central Cuba as of 21Z. The atmosphere remains very moist and
unstable over much of the area west of 61W, where scattered
showers and isolated thunderstorms are evident. Scattered showers
and thunderstorms are along the coast of Hispaniola west of 70W,
and along the southern portion of the surface trough. These
conditions are expected to change little through Tuesday. E of
70W, the atmosphere becomes very stable, except near the tropical
waves and tropical low as described above. The METEOSAT-9 imagery
shows an abundance of the Saharan Air Layer and associated dust
spreading westward over much of the eastern and central Atlantic
waters north of the tropical zone.

For additional information please visit
http://www.hurricanes.gov/marine

$$
Aguirre
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