[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 261006
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
606 AM EDT Wed Jul 26 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
0930 UTC.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis extending from
16N24W to 07N25W, moving westward at 10 kt. Although satellite
imagery shows that the wave lacks deep moisture as it remains
under Saharan dry air and dust, there appears to be a broad area
of mid-level clouds rotating counterclockwise over the area from
12N-15N between 22W-26W. The only convection related to the wave
is near where it crosses the monsoon trough. This convection
consists of the scattered moderate type intensity within 120 nm
south of the axis between the wave and 26W. Similar convection
is within 120 nm east of the wave from 10N-11.5N, and also west
of the wave within 30 nm of 10N28W.

An eastern Atlantic tropical wave has its axis extending from
14N35W to 04N36W, moving westward 10-15 kt. This wave is moving
through a very stable surrounding atmospheric environment marked
by Saharan dry air and dust north of 11N. The SSMI Total
Precipitable Water imagery (TPW) imagery indicates that deep
moisture with this wave is confined to south of 12N. Satellite
imagery shows minimal deep convection with this wave. Only
scattered moderate convection is where the wave crosses the
monsoon trough within 60 nm east of the wave.

A large amplitude central tropical wave has its axis extending
from near 24N52W to 18N52W to 12N53W, moving westward near 15 kt.
The northern portion of this wave is observed as a very
noticeable area of moisture as seen on SSMI TPW imagery. The wave
has a distinct signal at 650-700 mb as suggested in global model
guidance. Saharan dry air and dust is following in behind the wave
as seen in the latest METEOSAT-9 imagery. An easterly surge ahead
of the wave is passing underneath an area of upper level
diffluence that is situated to the southeast of an upper level
trough that located to the west of the wave and extends southwest
to the vicinity of the northeastern Caribbean Sea. Scattered
moderate isolated strong convection is moving quickly westward
with the surge from 09N-13N between 53W- 59W. This activity, if it
remains in tact, may be attendant by gusty winds as it moves over
portions of the Leeward Islands this afternoon and evening.
Scattered showers and isolated thunderstorms are within 60 nm east
of the wave from 20N- 23N. Isolated showers and thunderstorms are
within 60 nm elsewhere east of the wave.

An eastern Caribbean tropical wave has its axis along 65W south
of 19N, moving westward at 10-15 kt. The wave has a distinct moist
area as seen on SSMI TPW imagery south of 15N and north of 16N.
Broad 700 mb troughing is much of the eastern Caribbean. Since dry
air aloft is evident across the central portion of this wave as
seen in water vapor imagery, scattered showers and isolated
thunderstorms are mainly confined to within the moist areas
highlighted by the TPW imagery. The wave will move across the
remainder of the Caribbean through this evening, the central
Caribbean Thursday and Thursday night and across the eastern
portion of the western Caribbean on Friday.

...ITCZ/MONSOON TROUGH...

The monsoon trough axis extends from 13N16W to 10N24W to 10N30W
to 08N40W, where scatterometer data indicates the ITCZ begins and
continues to 08N46W to 10N51W. Besides convective activity
described above in association with the tropical waves, scattered
moderate isolated strong convection is within 60-90 nm north of
the monsoon trough between 26W-34W. Scattered moderate convection
is within 60 nm north of the monsoon trough between 38W-40W,
within 60 nm north of the ITCZ between 42W-45W and within 60 nm
north of the ITCZ between 45W-49W.

...DISCUSSION...

GULF OF MEXICO...

In the upper levels, an upper level low drifting northwestward
is centered over the western Gulf near 26N94W, with a trough
extending south-southwestward to 18N93W, and a second trough
extending northeastward to near 30N92W. Water vapor imagery shows
a markedly increased area of moisture covering the much of the
western portion of the Gulf. Ample moisture and instability
associated with the upper level low and first trough is resulting
in scattered showers and thunderstorms across the western half of
the Gulf south of 27N. Scattered showers and isolated
thunderstorms are noted south of 26N across the central and
eastern Gulf. Isolated showers and thunderstorms are over the
Yucatan Peninsula, while scattered showers and thunderstorms are
over much of southeastern Mexico. At the surface, a 1020 mb high
centered at 28N88W dominates the wind flow pattern across the
eastern and central portions of the Gulf, with light to gentle
anticyclonic winds. The typical Yucatan Peninsula thermal trough
has moved to the eastern Bay of Campeche. Little change is
expected with the current synoptic pattern over the next couple of
days.

CARIBBEAN SEA...

A tropical wave is over the eastern Caribbean. See above for
a discussion on this feature. In the upper levels, an upper
level low is centered over the SW Caribbean near 15N79W, with
a trough southwest to northern Panama. An anticyclone is just
north of the coast Venezuela at 11N65W, with associated
anticyclonic flow covering much of the eastern and central
Caribbean except for the northeast portion where the southern
portion of a central Atlantic upper trough is evident. Scattered
moderate to strong convection is quickly increasing over the far
SW Caribbean south of 12N and west of 79W, and also south of 10N
between the coast of Colombia and 79W due mainly to the presence
of the monsoon trough that extends from the eastern Pacific to
across Costa Rica and Panama and the nearby southern extent of an
upper level trough that stretches from Hispaniola to the SW
Caribbean. This activity contains frequent lightning. Scattered
showers and isolated thunderstorms are seen north of 15N between
67W-72W, and east of 67W associated with a tropical wave there as
discussed above. Isolated showers and thunderstorms are elsewhere
across the sea. The tropical wave moving through the eastern
Caribbean should provide additional moisture and instability that
portion of the sea and also the central and eastern portion of the
western Caribbean over the next 48 hours.

...HISPANIOLA...

Scattered showers and thunderstorms are seen just north of the
eastern  section of the Dominican Republic as an upper cyclonic
shear axis nearby is providing additional instability to an
already very moist and unstable environment present over the
island. Water vapor imagery depicts that moisture has increased in
the upper levels compared to the previous days. With plenty of
deep layer moisture and instability in place, and with the added
factor of the eastern Caribbean tropical wave forecast to pass
near the island within the next 48 hours, expect for deep
convection to become scattered to locally numerous over most
sections of Hispaniola through at least Thursday night. Some of
this activity may produce locally heavy rain and frequent
lightning.

ATLANTIC OCEAN...

In the upper levels, a large upper level low retrograding in a
general westward direction is identified to be over the central
Atlantic at 27N57W, with a trough stretching southwestward to
across the NE Caribbean Sea and to Hispaniola. Scattered moderate
convection is occurring from 20N-24N between 52W-58W. Scattered
showers and isolated thunderstorms are seen south of 27N between
58W-75W, and are moving westward. Isolated showers and
thunderstorms are elsewhere west of 70W. At the surface, a nearly
stationary 1026 mb high is centered over the central Atlantic
near 33N53W. To its east, a nearly stationary 1026 mb high is
centered over the eastern Atlantic near 32N41W. A broad ridge
covers most of the central and eastern Atlantic. A large area of
Saharan dust is present over the eastern Atlantic, and much of
the central Atlantic behind the tropical wave along 51W. In the
tropics, there are three tropical waves. See above for discussions
on these features. No major changes expected through next couple
of days.

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

$$
Aguirre
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