Tropical Weather Discussion
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AXNT20 KNHC 160005

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
805 PM EDT Sat Jul 15 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
2345 UTC.


A central Atlantic tropical wave has its axis extending from
14N44W to 04N45W, moving westward at 10-15 knots. The wave has
dry Saharan air well to the west of its axis as depicted in the
latest METEOSAT-9 Saharan Air Layer imagery as well to its east.
Scattered moderate isolated strong convection is within 180 nm
east and 120 nm west of the wave from 09N to 10N. This wave
may possibly acquire more convection early next week with
the possibility of low pressure forming along it.

A central Caribbean tropical wave has its axis extending from
19N69W to inland northwestern Venezuela at 12N72W, moving
westward near 20 kt. Streamline analysis from the GFS model
depicts 700 mb troughing over the general location of this wave.
Scattered moderate to strong convection is inland the coast of
Venezuela from 09N to 12N between 69W-71W. Scattered moderate
convection is east of the wave axis from 13N to 17N between
68W-70W. Scattered showers and isolated thunderstorms are ahead
of the wave to 75W from 14N to 17N. Some of this activity may
contain gusty winds. The wave is forecast to move across the
rest of the central Caribbean through Sunday afternoon, and
across the western Caribbean Sunday evening through Monday.

A western Caribbean tropical wave has its axis extending from
just south of western Cuba near 21.5N82W to 15N83W to inland
northern Costa Rica, moving westward at 15-20 knots. The northern
portion of the wave`s axis is lies to the east of a small upper
level low that is located between northwestern Cuba and the
Yucatan Peninsula. A cyclonic shear axis is evident extending
from the low to another small upper low over Jamaica. Deep
moisture along with ample instability present over the far
northern Caribbean to the north of 19N and west of Jamaica
including the environment over the northern portion of the wave is
combining to bring developing scattered showers and thunderstorms
north of 19N between 79W-82W. Very deep moisture over the far SW
Caribbean, some associated with the close proximity of the eastern
Pacific monsoon trough, is combining with instability provided by
the wave to produce scattered showers and thunderstorms south of
14N west of 79W. Isolated showers and thunderstorms are elsewhere
within 240 nm west and 180 nm east of the wave axis. This wave
will move across the remainder of the western Caribbean through
Sunday afternoon and inland the Yucatan Peninsula and central
America Sunday evening.


The Monsoon Trough axis extends from 12N17W to 09N30W to just
east of the tropical wave along the position from 14N46W to
04N48W. It resumes just west of the same wave to just northeast
of the coast of South America near 06N54W. Aside from the
convection related to the tropical wave along 47W, scattered
moderate isolated strong convection is within 120 nm north of
the axis between 35W-40W. Scattered moderate convection is within
240 nm south of the axis between 40W-46W, within 180 nm north of
the axis between 40W-43W, and within 60 nm south of the axis
between 22W-29W.

Scattered moderate to isolated strong convection is noted south
of the monsoon trough from 03N to 08N between 31W-39W.



A small upper level low is over the far northeast portion of the
Gulf at 29N85W, with a trough stretching southwestward from it to
another small upper level low over the far southwestern Gulf at
21N94W, moving westward. At the surface, a persistent surface
trough is analyzed over the central Gulf along a position from
29N88W to 22N89W, drifting westward. With these features in place,
abundant deep moisture and plenty of instability remain in place
over just about the entire basin, except for the far southeastern
portion where dry air aloft is advecting west-southwestward south
of 27N and east of 85W as seen in water vapor imagery. Latest
national mosaic radar display and satellite imagery show scattered
showers and thunderstorms north of 26N east of 92W. Isolated
showers and thunderstorms are noted elsewhere across the Gulf.
Scattered moderate to isolated strong convection is over much of
the northern and western sections of the Yucatan Peninsula due to
the daily thermal trough that becomes established there during the
afternoons. A rather weak pressure pattern is analyzed over the
area. The present moisture along with the induced shower and
thunderstorm activity will change little through at least Sunday
night. The western periphery of Atlantic high pressure is forecast
to protrude more westward across the eastern and central Gulf
later on Monday and into Tuesday.


A couple of tropical waves are moving through the Caribbean Sea.
See the section above for details. Aside from the convection
related to these waves, isolated showers and thunderstorms are
noted elsewhere over much of the sea. A relatively light pressure
gradient over the area is allowing for generally light to moderate
trades to exist across the sea, except for fresh to locally
trades over the south-central portion of the sea. Little change is
expected with these conditions into Monday. Moisture and resultant
convection is expected to be on the increase over the western
half of the sea and portions of central America through Monday.


Scattered moderate convection is occurring over much of the
interior portions of island early this evening as a result of
earlier afternoon heating and sea breeze. The northern portion of
a central Caribbean tropical wave is passing through the south-
central part of the island. Scattered showers and thunderstorms
are seen east and southeast of the wave. It is possible that some
of this activity will affect portions of the island through Sunday
as the wave advances westward.


A tropical wave is moving across the central Atlantic. See the
section above for details. A large upper level low lifting
northward is centered near 29N69W. A resultant surface trough
is along a position from near 32N65W to 22N66W. Scattered showers
and thunderstorms are seen north of 25N between 60W-65W, while
scattered showers and isolated thunderstorms are north of 26N
between 65W-73W. An upper trough extends from the low
southwestward to between Hispaniola and Cuba and to an upper
level low over Jamaica. Another upper level low moving westward is
over the eastern Atlantic near 28N45W, with a trough extending
south-southwestward to near 16N49W and to near 10N52W. Elsewhere
at the surface, a trough is over the central Bahamas along a
position from near 26N76W to inland central Cuba at 22N78W. This
trough is being supported by an upper level trough that extends
from the upper level low near 29N69W to the near the southeastern
and central Bahamas.  Plenty of moisture and instability over
waters south of 26N between 74W and 79W is inducing increasing
scattered showers and thunderstorms over those same waters
including the Bahamas and just about the entire island of Cuba.
The surface trough is forecast to slowly move westward through the
remainder of the Bahamas through Sunday, and reach southern
Florida Sunday night. The associated moisture along with the
shower and thunderstorm activity will translate westward with this

Otherwise, the remainder of the basin is under the influence of
a surface ridge, anchored by a 1026 mb high centered near 33N52W.
Abundant Saharan air and associated dust covers just about the
entire eastern Atlantic, and much of the central Atlantic areas
per latest METEOSAT-9 imagery. The dust is gradually migrating
westward as some has already entered the far eastern Caribbean

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