[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 311806
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
205 PM EDT Mon Jul 31 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 1200 UTC surface analysis and satellite imagery through
1745 UTC.

...SPECIAL FEATURES...

Tropical Storm Emily is approaching the mouth of Tampa Bay
centered near 27.6N 82.8W or about 30 nm SW of Tampa, Florida and
25 nm NW of Sarasota at 31/1500 UTC moving E at 8 kt. Estimated
minimum central pressure is 1005 mb. Maximum sustained wind speed
is 40 kt with gusts to 50 kt. Latest satellite imagery and
NWS mosaic doppler radar display reveal scattered moderate
isolated strong convection within 60 nm of the center in the
southeast semicircle including inland sections of west-central
Florida, and also from 24N to 27N east of 84W to inland much of
southern Florida. Scattered moderate convection seen within 15 nm
either side of a line from 25N84W to 26N85W to 26N88W denotes
outer- rain bands feeding into Emily. Emily is forecast to reach
the Florida west-central coast and reach to near 27.7N 81.6W by
early this evening while weakening to a depression. Emily is then
forecast to track across central Florida through tonight, and
offshore the east-central Florida coast Tuesday morning. The
cyclone is then forecast to track northeastward while regaining
strength to a minimal tropical storm near 28.9N 79.6W early on
Tuesday, to near 30.5N 77.7W by Tuesday evening and to near 32.2W
75.6W early on Wednesday with maximum sustained wind speed of 40
kt gusts to 50 kt. Emily is expected to produce total rain
accumulations of 2 to 4 inches through tonight along the west
coast of central Florida between the Tampa Bay area and Naples,
with isolated amounts up to 8 inches possible. Elsewhere across
central and south Florida, 1 to 2 inches of rain is expected with
localized amounts of up to 4 inches possible. See latest NHC
forecast/advisory under AWIPS/WMO headers MIATCMAT1/WTNT21 for
more details.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis extending from
19N24W to 13N23W to 07N22W, moving west 10-15 kt. First visible
satellite images show what appears to be a cyclonic vortex on the
northern end of the wave that tilts some to the west. This portion
of the wave is embedded in an extensive area of Saharan dry air
and dust. Moisture with this wave had increased during the
overnight hours south of 15N in the vicinity of the monsoon
trough, but has significantly diminished during the past few
hours. Only scattered showers and isolated thunderstorms are seen
240 nm east of the wave from 09N-16N and within 180 nm west of the
wave from 07N-11N.

A central Atlantic tropical wave has its axis extending from
18N45W to 12N45W to 06N42W, moving west near 16 kt. This wave is
well depicted on visible satellite imagery, and is marked by a
broad envelop of low clouds that shift from a southwest motion to
a northwest motion across the wave axis. The 700 mb guidance from
the GFS model indicated broad troughing over this wave, and
resembles the overall structure of the wave as observed on the
visible imagery. The wave is also void of deep convection as it is
being influenced by the intrusion of Saharan Air Layer that is
present over the eastern and central regions of the Atlantic.
Moisture noted with the wave is confined to where the axis crosses
the monsoon trough. Scattered moderate convection is within 120
nm west of the wave from 06N-09N. Scattered showers a
thunderstorms are within 180 nm east of the wave from 05N-11N.
This wave is forecast to move into the eastern Caribbean on
Wednesday attendant by scattered showers and thunderstorms.

An eastern Caribbean Sea tropical wave is along 67W/68W south of
19N, moving west at 15-20 kt. This wave is moving along the
southwest periphery of the sub-tropical Atlantic high pressure
ridge. The wave marks the leading edge of abundant dry Saharan
air and dust from the eastern Atlantic. A patch of moisture with
scattered showers and isolated thunderstorms trails the wave from
12N-15N and east to near 64W. Isolated showers and thunderstorms
are elsewhere within 240 nm either side of the wave. The tropical
wave will move across the remainder of the eastern Caribbean
through tonight, the central Caribbean Tuesday and Tuesday night
and the western Caribbean Wednesday.

...ITCZ/MONSOON TROUGH...

The monsoon trough axis extends from the west coast of African
coast near 19N16W to 12N25W to 11N37W to 10N52W, where
scatterometer data indicates that ITCZ begins and extends to
10N52W to 10N60W. Aside from convection associated with the
tropical waves as discussed above, scattered moderate to isolated
strong convection is within 180 nm south of the trough axis
between 30W-34W, and within 60 nm south of the ITCZ between
55W-58W. Scattered moderate convection is within 120 nm south of
the trough between 40W-42W and between 47W-50W, and within 60 nm
south of the ITCZ between 52W-55W.

...DISCUSSION...

GULF OF MEXICO...

The main feature is Tropical Storm Emily, which formed at 1200 UTC
this morning west of Tampa Bay. See the special features section
above for details on this tropical cyclone. In the upper levels, a
rather sharp deep layer trough stretches from along the
southeastern United States coastline to central Florida and to
just northeast of Emily. A large anticyclone over south-central
Texas dominates the upper flow pattern with its associated
anticyclonic flow covering just about the entire basin, except
near Emily where the upper trough related winds are more
noticeable. Water vapor imagery depicts very dry air pressing
south behind the upper trough. At the surface, a weakening
stationary front that earlier was attached to the low that spawned
the now Tropical Storm Emily is becoming diffuse from near 26N86W
to 26N93W to the coast of Texas near 28N97W. A weak pressure
pattern is analyzed over the Gulf outside the radii of Emily
associated winds and lower pressures. Scattered showers and
isolated thunderstorms are south of the diffusing the frontal
boundary to 24N between 88W-93W and within 90 nm south of the
boundary west of 93W. Although Tropical Storm Emily is forecast to
continue to move inland across central Florida tonight, expect
the convection over the SE Gulf to continue through Tuesday,
impacting much of southern Florida and the Keys through much of
Tuesday. The western periphery of Atlantic high pressure is then
expected to protrude westward across Florida and into the eastern
Gulf Tuesday night through Wednesday allowing for the deep
moisture and convection over the SE Gulf to decrease.

CARIBBEAN SEA...

A tropical wave is moving across the eastern Caribbean early this
afternoon. See above for details on this feature. The eastern
segment of the eastern Pacific monsoon trough extends east to the
SW Caribbean. Large clusters of scattered moderate isolated strong
convection are from 09N-14N west of 81W. Scattered showers and
thunderstorms are south of 13N between the coast of NW Colombia
and 81W. Some of this activity may contain strong gusty winds.
Aloft, a cyclonic shear axis extends from an elongated upper low
at 16N75W westward to 16N82W to inland northern Honduras. With
ample moisture in place across the central and western Caribbean,
instability associated with the cyclonic shear axis is producing
scattered showers and isolated thunderstorms from 15N-18N between
72W-8portions of Jamaica. Isolated showers and
thunderstorms are elsewhere west of 69W. The shower and
thunderstorm activity with the cyclonic shear axis will change
little through Tuesday, then begin to shift more towards the
western Caribbean Tuesday night through Wednesday as the upper
low retrogrades westward.

...HISPANIOLA...

Scattered showers and thunderstorms are over some locations of
the south-central portion of the island early this morning. This
activity is expected to move off to west-northwest through the
afternoon and evening as dry air aloft filters in from the east,
and the upper low to the southwest near 16N75W gradually pulls
farther away from the island. A tropical wave passing just to the
southwest of Puerto Rico is expected to bring a slight increase
of shower and thunderstorm activity on Tuesday to mainly the
southern portion of Hispaniola. This activity should be rather
short-lived as additional Saharan dry air behind the wave moves
in over the vicinity of the island. Afternoon widely scattered
showers and thunderstorms over higher terrain areas are expected
this afternoon, and Tuesday.

ATLANTIC OCEAN...

Two tropical waves are moving across the tropical North Atlantic.
See tropical waves section above. A stationary front extends from
32N77W southwest to a 1022 mb low at 30N80W, and continues
southwest to across central Florida. The sharp deep layer trough
that supports the front also supports a large area of scattered
moderate isolated strong convection that is confined to the waters
from the cental Bahamas to 30N and between 76W-79W. Similar
activity is noted from 25N-27N west of the Bahamas to across
southern Florida, and also over central Florida ahead of Emily.
Little change is expected with the trend of this convection being
active through Wednesday as the upper trough slowly flattens out.
Emily is forecast to track from central Florida to offshore the
east-central Florida coast on Tuesday morning near a position of
28.9N 79.6W, to near 30.5N 77.7W by Tuesday evening and to near
32.2W 75.6W early on Wednesday with maximum sustained wind speed
of 40 kt gusts to 50 kt. Winds and seas near the periphery of
tropical storm force winds associated with Emily are expected to
be impacted with passing squalls and thunderstorms. Otherwise, a
large 1029 mb high centered over the central Atlantic near 33N43W
will maintian generally stable weather conditions east of about
through 68W. Abundant Saharan air and dust will continue east of
66W.

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

$$
Aguirre
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