[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 071127
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
727 AM EDT Fri Jul 7 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 0600 UTC surface analysis and satellite imagery through
1115 UTC.

...SPECIAL FEATURES...

Tropical Depression Four is centered near 15.0N 48.8W at 07/0900
UTC or about 725 nm east of the Lesser Antilles moving WNW at 19
kt. Estimated minimum central pressure is 1011 mb. The cloud and
convective structure of the depression appears more symmetrical
compared to yesterday and last night as observed on latest
satellite imagery. The imagery reveals 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 maintain intensity through Saturday,
then weaken to a post-tropical/remnant low late Saturday night
near 20.1N 61.9W as westerly vertical wind shear increases over
it. 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 16N21W to 11N22W to 05N22W, moving westward at
10 kt. 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 to isolated
strong type within 180 nm east and 120 nm west of the axis from
06N-08N.

A tropical wave is over the eastern Caribbean Sea with axis
extending from 20N63W to 15N63W to inland northeastern Venezuela
at 07N63W, moving westward near 18 kt. 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 either side 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 is analyzed over the far western Caribbean Sea
with axis extending from near 22N86W south to inland the northwest
portion of Honduras at 16N87W, 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, but
should begin to soon slow down. 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. Similar activity is east of the wave from along
the northeastern coast of Honduras north to 18N. Isolated showers
and thunderstorms are west of the axis north of 18N, and elsewhere
east of the axis to 84W 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 99W. 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 isolated strong convection is within 120 nm north of the axis
between 37W-43W. Similar activity is within 60 nm south of the
axis between 37W-44W. Scattered moderate convection is within 120
nm north of the axis between 24W-26W, within 60 nm north of the
axis between 17W-19W and within 60 nm south of the axis between
34W-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 1019 mb high is centered
over the NE Gulf near 29N85W as of 0900 UTC with associated light
to moderate anticyclonic flow covering the eastern Gulf north of
28N and east of 87W. Isolated showers and thunderstorms are
indicated on mosaic national radar imagery to be present over the
eastern Gulf east of 85W and south 28N. This activity is moving
in a west-northwestward direction. Model guidance indicates that
moisture will be on the increase through the weekend allowing for
more convection to develop over much of the basin.

CARIBBEAN SEA...

A tropical wave is about to move inland as it extends from along
the Yucatan Peninsula southward to inland the northwestern section
of Honduras. Another tropical wave is over the eastern Caribbean.
See above for further details on these tropical waves. Scattered
moderate convection is within 30 nm either side of a line that
extends from just inland southeastern Nicaragua to near 10N80W.
This activity is within close proximity of the eastern Pacific
monsoon trough that stretches into northwestern Colombia. In the
upper levels, broad anticyclonic flow covers the western
Caribbean, while a small upper level low is centered over central
Caribbean near 14N72W. 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 10-20 kt
trades with the strongest in the 20-25 kt range along the coast
of NW Colombia where the gradient is the tightest.

...HISPANIOLA...

Latest water vapor imagery shows dry air aloft advecting westward
from the eastern Atlantic to across portions of the eastern and
central Caribbean Sea, including Hispaniola. This is presently
keeping weather conditions on the quite side over and near the
island. The tropical wave currently over the eastern Caribbean
is forecast to pass through the area Saturday, and may bring
an increase of moisture to the island. The amount of moisture
will depend on just how prevalent the dry air will be at that
time. At most, brief passing low-topped showers are possible
through the weekend mainly near the southern portions of the
island. If some of the moisture were to spread more northward
over the interior of the island, then this may combine with local
effects to bring an increase of scattered showers and
thunderstorms to interior portions of the island through the
weekend.


ATLANTIC OCEAN...

Tropical Depression Four and a tropical wave are analyzed over
the tropical Atlantic. See above for further details. An area of
scattered showers and isolated thunderstorms, possibly related to
a low-level trough, is moving westward to the northwest of
Tropical Depression Four. This activity is observed from 19N-21N
between 49W-53W. The upper flow related to an upper low over the
eastern Gulf of Mexico is drawing abundant moisture northward
across the much of the Bahamas and waters between the Bahamas
and southern Florida. This has resulted in scattered showers and
isolated thunderstorms across these waters. Dual surface highs,
one of 1029 mb and the other of 1030 mb, are centered north and
northeast of the discussion area near 35N36W and 37N29W,
respectively. The associated high pressure ridge extends into
the area through 32N47W and to central Florida, and is the main
feature in control of the wind regime throughout. 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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