[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 282342
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
742 PM EDT Fri Jul 28 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
2315 UTC.

...TROPICAL WAVES...

A central Atlantic tropical wave extends from 17N38W to a 1012 mb
surface low centered near 11N38W to 04N37W, moving westward at 10
kt. Both satellite imagery and the total precipitable water (TPW)
imagery animation reveal that significant moisture was noted in a
narrow swath within 120-180 nm either side of the wave axis. A
large area of Saharan Air lies to the east of the wave axis.
Scattered low topped showers are noted within 120 nm of the low
circulation.

A west-central Atlantic tropical wave extends from 20N50W to
04N51W, moving west at 10 to 15 kt. This wave is moving through a
very stable atmospheric environment marked by the presence of a
very pronounced African Saharan Air Layer (SAL) that covers the
eastern and central Atlantic north of the tropics. Latest water
vapor imagery confirms that strong subsidence and resultant dry
air prevails over the the northern and central portions of this
wave. Isolated showers and thunderstorms were noted east of the
wave's axis S of 10N between 40W-48W.

An eastern Caribbean tropical wave along 67W, and extends
northward to the Atlantic near 21N. Water vapor imagery depicts
dry subsident air over the wave. No convection is occurring with
this wave at this time. This wave will move across the remainder
of the eastern Caribbean through tonight, then through the central
Caribbean on Saturday.

A western Caribbean tropical wave has is along 81W south of 20N.
The wave is moving west at about 15 kt. The southern portion of
the wave is aiding scattered moderate to strong convection over
Central America and the adjacent Caribbean west of 81W. The wave
will move across the rest of the western Caribbean through tonight
and inland over central America on Saturday.

...ITCZ/MONSOON TROUGH...

The monsoon trough extends from 14N16W to 12N20W to the 1012 mb
low at 11N38W to 09N43W. A segment of the ITCZ extends from 09N43W
to 09N51W. Aside from convection related to the tropical wave
described above, scattered moderate isolated strong convection is
within 240 nm to the south of the monsoon trough from the African
coast to 25W.

...DISCUSSION...

GULF OF MEXICO...

A surface ridge prevails across the basin anchored by a 1017 mb
high centered near 27N93W. A broad weak surface trough extended
from Pensacola, Florida to near 26N88W. Water vapor imagery and
satellite derived winds indicated anticyclonic flow covered most
of the Gulf anchored to an anticyclone over eastern Oklahoma. Deep
layered subsidence accompanied the flow over the Gulf west of 90W
while upper level moisture was sweeping across areas east of 90W.
An upper-level low centered over western Cuba was enhancing
convection over the island while upper level diffluent flow
between the two features coupled with the afternoon seabreeze was
enhancing convection over east-central Florida. Scatterometer and
surface observational data depicted light to gentle winds across
the basin with seas generally 1 to 2 FT. A fairly deep mid to
upper level trough for mid-summer will push a cold front southward
to the deep south by late Sat with an increase in showers and
thunderstorms along the Gulf coast. The front itself will enter
the northern Gulf on Sun with winds shifting to the north.
Increasing SW to W winds will develop south of the front over the
Gulf to 25N.

CARIBBEAN SEA...

Two tropical waves are moving across the basin. Refer to the
section above for details on these features.ers are
observed across the western Caribbean on the southern periphery
of an upper-level low centered over central Cuba, as seen in
water vapor imagery. Scattered to numerous moderate and strong
convection is noted over the southwest Caribbean south of 12N
between 80W-83W. This activity is occurring along the eastern
extension of the Pacific monsoon trough and the tropical wave
along 81W. This activity is being further aided by upper
diffluent flow between the southern extent of an upper trough
located over the NW Caribbean and an anticyclone over Panama.
Other areas of orographically forced convection were noted over
Cuba, Hispaniola and Puerto Rico. The activity appears to have
peaked with weakening trends in place. Scatterometer data
indicated fresh to strong trades over the south- central Caribbean
with generally light winds over the western portion of the basin.
Little change in the overall conditions is expected through the
weekend.

...HISPANIOLA...

The 1200 UTC rawindsonde from Santo Domingo showed limited
moisture with generally light winds through the entire column up
to 200 mb. The profile suggests any thunderstorm activity that
develops would be primarily orographically forced and quasi-
stationary. Currently clusters of quasi-stationary strong
thunderstorms over the interior of Haiti and the Dominican
Republic are in the process of weakening. Moisture should
increase slightly Saturday as the present eastern Caribbean
tropical wave passes through the central Caribbean. Some pockets
of dry air behind the wave will follow in behind the wave.

ATLANTIC OCEAN...

Two tropical waves are moving across the basin. Refer to the
section above for details. The upper-level low centered over
western Cuba extends northeast enhancing convection across the
southern Bahamas and Florida Straits. This activity is expected to
lift northward on Saturday in response to a frontal boundary that
will push off the southeastern United States and move to the
northwest portion of the basin late Saturday through Sunday. To
the east, another upper- level low near 27N58W is reflected at
the surface as a trough that extends from 31N56W to 25N57W. Widely
scattered showers are observed along this trough. The upper low is
sliding eastward at 10 kt. The remainder of the basin is under
the influence of a surface ridge anchored by a 1024 mb high
centered near 30N38W.

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

$$
Cobb
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