Tropical Weather Discussion

axnt20 knhc 211735

Tropical weather discussion
NWS National Hurricane Center Miami FL
135 PM EDT Thu Jun 21 2018

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 
1715 UTC.

...Tropical waves...

As of 1200 UTC, there are four tropical waves between the West 
Coast of Africa and the Lesser Antilles. 

A tropical wave is along 25w from 03n-12n, moving W at 20 kt. The
hovmoller diagram shows the westward propagation of the wave, 
that coincides with a modest surge of moistened air based on the 
tpw product. Abundant cloudiness surrounds the wave's axis but 
convection is limited.

A tropical wave is along 34w from 3n-11n, moving W at 20 kt. This
wave shows up well as a low amplitude moisture surge on the tpw 
animation. Scattered showers are noted where the wave meets the 

A tropical wave is along 43w from 3n-11n, moving W at about 15 
knots. The wave is well depicted in the moisture product, and
model diagnostics guidance. Scattered moderate convection is 
noted on either side of the wave's axis from 6n-8n between 40w- 

Another tropical wave is along 60w from 6n-17n, moving W at about
10 knots. The wave coincides with a high amplitude northward bulge
of moisture, and is also well depicted in model diagnostics 
guidance. Scattered moderate convection is already affecting 
Trinidad and Tobago as well as Barbados, where showers and some 
tstms have been reported. Moisture associated with this feature 
will continue to affect the Windward Islands today. The wave will 
then move across the eastern Caribbean this afternoon through Fri 
night. The associated moisture is forecast by the GFS computer 
model to spread out reaching the Leeward Islands later today and 
tonight, and Puerto Rico on Fri, then Dominican Republic Fri night
into Sat.

A tropical wave is moving across the Caribbean Sea. Its axis is 
along 73w, and extends from Hispaniola to northern Colombia. 
The wave is interacting with an upper-level trough that crosses 
eastern Cuba. Lingering moisture from this tropical wave will 
continue to support scattered showers and isolated thunderstorms 
across Hispaniola today. Moisture and instability related to this 
wave will also affect the Windward Passage and eastern Cuba, 
as well as Jamaica today. Currently, scattered showers and tstms 
are noted in the Windward Passage, across the waters between 
eastern Cuba and Jamaica, and E of Jamaica. This wave is forecast 
to move across Jamaica tonight, entering the western Caribbean 

...Monsoon trough/ITCZ...

the monsoon trough passes through the coastal sections of Guinea
near 10n13w to 06n29w. The ITCZ continues from 06n29w to 06n30w 
05n40w to 05n50w to 06n57w. Outside of the convection associated 
with the tropical waves, isolated moderate convection is from 3n- 
7n between 24w-35w. Scattered moderate convection is from 6n-8n 
between 55w-58w.


Gulf of Mexico...

A 1007 mb low pressure centered along the Texas/NE Mexico border
near 27n99w continues to produce a large area of showers with
embedded tstms over the western Gulf Coast and NE Mexico,
particularly over the states of nuevo Leon and tamaulipas, where
heavy rain has been reported. This slow moving system will 
continue to generate rounds of rainfall across the western Gulf
Coast from Texas to western Louisiana today. Flooding of low lying
and poor drainage areas will be possible. Winds and seas in the 
NW Gulf will diminish further today as the low weakens. 

A 1016 mb high pressure is analyzed over the se Gulf near 24n86w.
A broad ridge will persist over this area, and support light winds
and seas less than 3 ft east of 88w through the upcoming weekend.

A surface trough will develop in the Yucatan Peninsula each 
afternoon, then move westward across the SW Gulf during the 
overnight hours, accompanied by fresh to occasionally strong east
to southeast winds.

Caribbean Sea...

A tropical wave is moving across the central Caribbean. Another 
tropical wave has reached the Windward Islands. Wind observations
from these islands clearly show the wind shift associated with 
the wave's axis. Please, see tropical waves section for details. 
Expect increasing showers and isolated thunderstorms in 
association with the passage of these tropical waves.

High pressure N of area is forecast to strengthen over the next
couple of days while moving westward. As a result, the trade 
winds over the south-central Caribbean will strengthen and expand
in areal coverage across the basin through early next week. Winds
could reach near gale force along the coast of Colombia by Sun 
night. Fresh to strong winds will affect the Gulf of Honduras 
each night beginning tonight through Mon night. 

An upper-level trough extends from a cyclonic circulation located
over the western Atlantic near 27n65w to another cyclonic circulation
over the NW Caribbean and the Yucatan Peninsula. A diffluent pattern
aloft between this trough and an anticyclonic circulation over the
south-central Caribbean is helping to support scattered showers
and tstms across the Caribbean waters from 15n-20n between the
tropical wave along 73w and 85w. Lightning density indicates
frequent lightning with some of the observed convection. As of
1500 UTC, a trough, surface reflection of the upper-level low is
analyzed over the NW Caribbean, and extends from 20n85w to the 
Gulf of Honduras. Abundant tropical moisture will persist across
the NW Caribbean and the Yucatan Peninsula on Fri.

Atlantic Ocean...

An upper-level trough extends from a cyclonic circulation centered
near 27n65w to eastern Cuba. Scattered showers and tstms are 
noted on the se semicircle of the low affecting mainly the waters
from 24n-29n between 60w and 70w. A diffluent pattern aloft 
between the aforementioned upper-level trough and an anticyclonic
circulation located E of the Lesser Antilles is helping to induce
this convective activity. Lightning data also indicate frequent 
lightning with some of the perceived convection.

High pressure of 1029 mb centered near 33n34w extends a ridge
across the forecast area. Fresh trades are noted along the
southern periphery of the ridge, but mainly between 40w-70w. This
high pressure will slowly shift westward through Sat night, then 
remain nearly stationary near 30n55w through Tue. The tightening 
pressure gradient that results over the central Atlantic will 
support fresh to strong trade winds and seas of 8-10 ft E of the 
Lesser Antilles to about 45w by early Sat morning. These marine
conditions will persist on sun.

The Saharan air layer (sal) from CIMSS and visible satellite 
imagery confirme the presence of African dust between the West 
Coast of Africa and the Lesser Antilles, more concentrated E of 

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