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Atlantic Tropical Weather Discussion

AXNT20 KNHC 241057

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
657 AM EDT Mon Jul 24 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 
1030 UTC.


An eastern Atlantic tropical wave has its axis extending from 
17N26W to 05N25.5W, moving westward at 15 kt. Both CIRA LPW and 
SSMI TPW imagery confirms the extensive presence of dry air 
mainly in the northern wave's environment. Convection associated 
with this wave remains at a minimum as dry air to the north of the
wave has filtered some into its environment. Only scattered 
moderate convection is seen within 120 nm either side of the wave 
along and near the monsoon trough from 05N-08N. 

A central Atlantic tropical wave has its axis extending from 
21N40W to 15N39W to 09N39W, moving westward at 15 kt. This wave 
has a broad low-level cloud field associated with it, and is 
depicted in a somewhat inverted-V shape pattern as seen in the 
first visible satellite images. No deep convection is noted with 
this wave as the Saharan Air Layer (SAL) and associated dust has 
also mixed in with this wave's environment. Only isolated showers 
and weak isolated thunderstorms are noted east of the wave within 
30 nm of 17N39W.

Another tropical wave has its axis extending from 17N52W to 
06N53W, moving westward at 15-20 kt. Moisture has increased 
during the overnight hours mainly west of the wave as upper 
level dynamics provided by an upper trough that extends east
to west across the wave is providing additional instability and
lift to the environment around the wave south of 14N. Latest 
satellite imagery shows increasing scattered moderate convection 
within 45 nm either side of line from 12N52W to 12N56W to 12N58W.
Similar activity is east of the wave within 30 nm either side of 
line from 13N50W to 12N53W. A swath of Saharan dry air and dust is
present over and around this wave north of 14N.

The northern portion of an eastern Pacific tropical wave has moved
inland central America to over Guatemala and the far south-central
part of the Yucatan Peninsula. It is moving westward at 10-15 kt.
The Total Precipitable Water (TPW) imagery animation continues to
display abundant deep atmospheric moisture within the environment
of this wave. This moisture is seen in infra-red satellite 
imagery as mainly broken to overcast mid to high level debris 
cloudiness from previous deep convective activity. Scattered 
strong convection has recently developed over far southeastern 
Belize and far northwestern Honduras. Scattered moderate 
convection is just offshore the northeast part of the Yucatan 
Peninsula within 30 nm of a line from 20N85W to 21N87W. Isolated 
showers and thunderstorms are over some areas of the Yucatan 
Peninsula. This activity is likely to become scattered to locally 
numerous this afternoon and into this evening.


The monsoon trough axis extends from 13N17W to 08N29W to 07N36W, 
where latest scatterometer winds then indicate the ITCZ begins 
and continues to 06N43W to near 06N51W. It resumes at 07N53W to
near the coast of South America at 07N57W. Aside from convection 
with the tropical waves, scattered moderate convection is within 
60 nm south of the trough axis between 28W-34W, and within 60 nm 
south of the ITCZ between 46W-51W. Similar convection is within 
120 nm north of the ITCZ between 45W- 51W, and within 60 nm south 
of the ITCZ between 42W-45W. 



Weak surface ridging dominates across the Gulf waters anchored by
western Atlantic high pressure. With this, light to gentle 
anticyclonic winds prevail across the basin. A small upper level
low is located over the central Gulf near 26N91W. A swath of dry 
air is evident within about 420 nm either side of the low from 
24N-27N, while moisture is seen north of 27N and south of 24N. 
Isolated showers and thunderstorms are within the moisture
areas. Scattered showers and isolated thunderstorms are occurring 
south of 24N between 85W-91W, and south of 22N west of 91W.
Similar activity is quickly developing over the NE Gulf north
of 27N and east of 86W, and also north of 28N between 86W-89W.
With little change expected in the current synoptic pattern 
through the next 24-48 hours, expect scattered showers and 
thunderstorms to pretty much develop over mainly the southern 
and northern waters, with isolated showers and thunderstorms 
possible elsewhere. A thermal trough will move westward from the 
Yucatan Peninsula into the Bay of Campeche with convection every 
evening. This trough will be enhanced some by the northern part of
a tropical wave that is currently along the coast of the southern
Yucatan Peninsula.


A tropical wave has moved further inland central America this
morning. Refer to the section above for details. A very moist and 
unstable atmosphere over the western portion of the Caribbean 
is leading to clusters of scattered moderate convection there,
and over the waters between eastern Cuba and Jamaica. In 
addition, the eastern Pacific monsoon trough extends along 10N to 
NW Colombia. This continues to enhance scattered shower and 
thunderstorm activity over the far SW Caribbean south of 13N and 
west of 80W to near the coasts of Costa Rica and Panama. All of 
this activity is expected to remain active over the next 48 hours 
or so. Elsewhere, a broad high pressure over the Atlantic
stretches across the basin supporting fair weather and 
maintaining a pressure gradient to support fresh to near
gale-force winds in the south-central Caribbean through early 
this morning and again late tonight.


With dry sinking air aloft advecting westward across the island,
only isolated showers and thunderstorms are possible just offshore 
the island. Conditions should become generally fair during the 
rest of the morning and into much of the the afternoon. Scattered 
showers and thunderstorms are expected to redevelop with daytime 
heating combining with local island effects today and again on 
Tuesday. This activity may be limited in coverage, and it is 
possible some of it may linger into the evening hours before it 


Three tropical waves are moving across the basin. Refer to the
section above for details. An upper-level low lifting
northeastward is north of the area at 33N74W, with a trough 
extending south-southwestward to the SE Bahamas and to 
southeastern Cuba continues to support scattered showers and 
thunderstorms over the northwest portion of the basin. This
activity is shifting eastward with time. A large upper-level low 
moving westward is near 24N45W. A resultant surface trough is 
along a position from 31N50W to 23N52W. Scattered showers and 
isolated thunderstorms are within 120 nm west of the trough from 
25N-28N, and also to the southwest of the trough from 20N-23N 
between between 55W-60W. The remainder of the basin is under the 
influence of a broad surface ridge anchored by a 1022 mb high 
centered near 29N61W. Very stable and dry conditions are observed 
north of 13N east of 50W where METEOSAT-9 imagery depicts an 
extensive area of Saharan dust that is pressing westward. No major
changes expected through next couple of days.

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