[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 070946 AAA
TWDAT

Tropical Weather Discussion...updated
NWS National Hurricane Center Miami FL
546 AM EDT Fri Jul 7 2017

updated Special Features for convection

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 0000 UTC surface analysis and satellite imagery through
0915 UTC.

...SPECIAL FEATURES...updated

Tropical Depression Four is centered near 13.4N 46.7W at 07/0300
UTC or about 855 nm east of the Lesser Antilles moving W or 20
kt. Estimated minimum central pressure is 1012 mb. The
depression is poorly organized as noted in latest satellite
imagery. Its convective and cloud pattern has become more
symmetrical during the overnight hours. The satellite imagery
shows scattered moderate to strong convection within 90 nm of
the center in the north and northeast quadrants. Scattered
moderate convection is within 75 nm of the center in the
southeast and south quadrants. The depression is expected to
continue to weaken today as dry air continues to be entrained
into its circulation. The latest NHC advisory forecasts for it
to degenerate to a remnant low by this evening, but it could
also open up into a tropical wave at any time before that time.
Please see the latest NHC Public Advisory under AWIPS/WMO
headers MIATCPAT4/WTNT34 KNHC and the full Forecast/Advisory
under the AWIPS/WMO headers MIATCMAT4/WTNT24 KNHC for more
details.

...TROPICAL WAVES...

A tropical wave is over the far eastern Atlantic with its axis
extending from 16N20W to 11N21W to 05N21W, moving westward at
5-10 kt during the past 24 hours. The wave is in a region of
favorable to neutral wind shear. However, extensive intrusion of
Saharan dry air and dust into the wave's environment continues to
presently suppress deep convection N of 08N. Observed convection
is within and near the monsoon trough, and consists of the
scattered moderate type within 60 nm east of the axis from 06N-
08N and also within 120 nm west of the axis from 06N-8N.

A tropical wave is over the eastern Caribbean Sea with axis
extending from 20N61W to 15N62W to inland northeastern Venezuela
at 08N62W, moving W around 15 kt during the past 24 hours. The
wave crossed the Lesser Antilles on Thursday evening as noted in
the surface observations. The CIRA mid-level satellite moisture
animation suggests that mid-level dry air is present across the
wave's environment, and the Metosat-9 imagery confirms the
presence of the dry air in showing a broken swath of eastern
Atlantic Saharan African dust that protrudes into the eastern
Caribbean Sea. The moisture present at the lower levels is
shallow, and latest satellite imagery shows scattered showers
and thunderstorms within 60 nm east and 90 nm west of the axis
south of 13N. Only isolated showers and thunderstorms are within
30-60 nm of the axis north of 13N. The wave is forecast to move
across the eastern Caribbean through Saturday night, and across
the eastern portion of the central Caribbean on Saturday. Expect
increasing moisture along with some pockets of scattered showers
and thunderstorms behind the wave.

A tropical wave analyzed over the western Caribbean Sea with axis
extending from near 22N85W south to inland central Honduras at
16N86W, and continues southward to the eastern Pacific waters
just west of northern Costa Rica. It has moved westward at about
20-25 kt during the past 24 hours. The wave is in a region of
unfavorable wind shear. However, shallow moisture and upper level
diffluent flow between an upper level low over the eastern Gulf
of Mexico, and a broad ridge noted over the western Caribbean
support scattered moderate to isolated strong convection west of
the wave axis south of 18N. Isolated showers and thunderstorms
are elsewhere west of the axis and within 120 nm east of the
axis as the atmospheric environment remains very moist and
unstable over the much of the western Caribbean Sea.

A tropical wave has moved inland eastern Mexico near 98W. The
flow pattern between an upper level low over central Mexico and
broad upper level ridging over the SW Gulf of Mexico supports
scattered moderate to isolated strong convection south of 24N
and west of 91W, including the Bay of Campeche.

...ITCZ/MONSOON TROUGH...

The Monsoon Trough axis extends from 13N17W to 06N23W to 04N30W.
The Intertropical Convergence Zone extends from 04N30W to 03N40W
to 07N47W to 09N53W to 10N58W. Aside from the convection related
to the tropical wave off the coast of Africa, scattered moderate
to strong convection is within 120 nm south of the axis between
37W-43W. Scattered moderate convection is within 120 nm north of
the axis between 23W-27W, within 60 nm south of the axis between
27W-30W, and within 60 nm south of the axis between 33W-37W.

...DISCUSSION...

GULF OF MEXICO...

A tropical wave has moved inland eastern Mexico. A very moist and
unstable environment east of the wave in combination with the the
flow pattern set-up between an upper level low over the central
Gulf and broad upper ridging over the SW Gulf is supporting
scattered moderate to isolated strong convection south of 24N and
west of 91W, including the Bay of Campeche. This activity is
expected to continue into Saturday. A 1020 mb high is centered
over the NE Gulf near 28N85W with associated light to moderate
anticyclonic flow covering the eastern Gulf north of 28N and east
of 87W. Isolated showers and thunderstorms are noted on mosaic
national radar imagery to be present over the eastern Gulf east
of 85W and south 29N. This activity is moving in a west-
northwestward direction.

CARIBBEAN SEA...

A tropical wave is moving across the western Caribbean, while
another tropical wave is over the far eastern Caribbean. See
above for further details on these waves. Scattered moderate
convection noted earlier over the interior of Cuba has just about
dissipated, except for lingering isolated weak activity over the
central portion of the island. Scattered moderate convection is
along the coast of Costa Rica, southern Honduras and northern
Panama. In the upper levels, broad anticyclonic flow covers the
western Caribbean, while a small upper level low is centered over
central Caribbean near 13N72W. Upper southerly flow over the
eastern portion of the low is transporting upper moisture from
northeastern Venezuela to across the eastern Caribbean, but most
of it dissipates in the dry air that has moved in from the
central Atlantic. The pressure gradient throughout supports 10-
25 kt trades with the strongest winds along the coast of NW
Colombia.

...HISPANIOLA...

Convection that occurred over the higher elevations of Haiti on
Thursday afternoon and evening has dissipated. Expect Hispaniola
to have a decrease in convection over the next 24 hours as the
island is in between tropical waves, and dry aloft advecting from
the east is settling in over the island

ATLANTIC OCEAN...

Tropical Depression Four and a tropical wave are analyzed over
the tropical Atlantic. See above. An area of scattered showers
and isolated thunderstorms moving westward is observed to the
northwest of Tropical Depression Four from 18N-21N between 49W-
52W. A surface trough is over the NW Bahamas with scattered
showers and isolated thunderstorms to its west. A broad 1029 mb
surface high is centered north of our area near 36N35W producing
fair weather. An extensive area of African Saharan dust is
situated over the eastern and central Atlantic, and is gradually
shifting westward as strong easterly winds aloft are present to
the south of the upper level anticyclone located over those
portions of the Atlantic. This synoptic pattern will change
little through the next couple of days.

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

$$
Aguirre
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