Tropical Weather Discussion
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AXNT20 KNHC 191816 CCA

Tropical Weather Discussion..corrected
NWS National Hurricane Center Miami FL
205 PM EDT Wed Jul 19 2017

Corrected Caribbean and Atlantic Ocean sections

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
1745 UTC.


A tropical wave is over the far eastern Atlantic with its axis
extending from near 15N20W to 06N21W moving westward 15-20 kt. The
wave remains embedded in a deep pool of moisture as seen in the
SSMI Total Precipitable Water imagery (TPW), and in the latest
CIRA low-mid level moisture imagery. The 700 mb streamline
guidance from the GFS indicates a well-defined 700 mb broad trough
in the vicinity of the wave. Scattered moderate isolated strong
convection is east of the wave to the coast of Africa from 08N-

A large central Atlantic tropical wave with its axis extending
from near 22N41W to 15N43W to low pressure of 1012 mb on the wave
axis at 11.5N44W to 05N45W. This system is moving in a general
westward to west-northwestward direction at about 12 kt. The wave
continues to exhibit a very large envelop of cyclonic rotation as
observed in the low cloud motion. Latest satellite imagery shows
that there has been some increase in deep level moisture with
this system during the past several hours. Scattered moderate
convection is seen from 10N-12N between 44W-47W, and within 30 nm
of line from 16N40W to 17N41W. According to the latest NHC
Tropical Weather Outlook some gradual development of this system
is possible during the next couple of days as it maintains its
current motion.

A tropical wave over the eastern Caribbean Sea has been introduced
to 12 UTC surface analysis. This wave denotes the remnants of
recent Tropical Storm Don. The wave is analyzed from near 16N66W
to a 1012 mb low to just north of Isla Margarita. The wave and low
are moving westward at 20-25 kt. Both Total Precipitable Water
imagery and satellite imagery depict the wave and low to be within
an area of very deep moisture south of 15N. Scattered showers and
isolated thunderstorms are within 180 nm east of the wave and
low. To the north of 15N, the atmosphere is very dry under a
Saharan Air Layer that has migrated westward over the eastern
Caribbean in the wake of the following wave described below. The
low pressure is forecast to dissipate in about 24 hours, while the
wave will continue through the rest of eastern Caribbean through
this evening, and the central Caribbean on Thursday. Fresh to
strong east winds will follow in the wake of the wave.

A tropical wave is across the central Caribbean along 72W
southward to inland Venezuela at  It is moving westward at about
20 kt. Similarly to the wave located to its east discussed above,
this wave is embedded within an area of very deep moisture south
of 15N, and is under Saharan Air Layer and dust north of 15N.
Latest satellite imagery shows scattered moderate isolated
convection moving quickly to the west behind the wave, and
consists of the scattered moderate to isolated type intensity
activity from 12N-14N between 66W and the wave. This activity
has the capability to produce strong gusty winds and very
rainfall. The visible imagery denotes the leading edge of
the convection as outflow boundaries racing westward along the
wave axis south of 15N.


The monsoon trough axis extends from 12N16W to 07N25W to 12N41W
to 09N48W. The ITCZ then extends from 09N48W to 06N56W. Aside
from the convection associated with the tropical waves, scattered
moderate isolated strong convection is within 120 nm north of the
trough axis between 23W-27W.



In the upper levels, an upper level low lifting northward is
centered over Mexico near 23N98W. Upper level diffluence to the
southeast of the low is supporting scattered moderate convection
over the far western Gulf from 21N-24N west of 94W. This activity
will remain active through the rest of the afternoon and into
tonight. A mid/upper trough just inland the north and northeast
Gulf is helping to support scattered showers and thunderstorms
north of 27N between 86W and 91W. At the surface, the Yucatan
Peninsula thermal trough pushed westward to the central Bay of
Campeche last night, and extends from 21N93W to inland Mexico at
18N94W at 12 UTC. Scattered showers and isolated thunderstorms
within 180 nm either side of the trough. Elsewhere, a 1019 mb high
center is over the central Gulf at 26N88W. This feature remains
in control of the wind regime throughout, with the associated
gradient providing mainly gentle anticyclonic flow throughout.


The main feature of concern over the southeastern Caribbean is
the remnants of Don as discussed above. Scattered moderate to
isolated trong convection is inland over SE Venezuela, and over
N Colombia. Scattered moderate to strong convection is over the
SW Caribbean S of 11N. Elsewhere, scattered moderate isolated
strong convection over the SW Caribbean will remain quite active
through Friday due to the combination of an upper level low near
19N82W and instability associated with the monsoon trough
axis across Costa Rica and Panama.


A fast moving tropical wave is moving across the central
portion of the island. Only isolated showers and thunderstorms
are noted over the interior of the island. Some increase of this
activity may occur during the remainder of the afternoon.


Scattered showers are over the N Bahamas and the W Atlantic, N of
25N and W of 73W. A large 1027 mb high is centered over the
central Atlantic near 32N58W producing fair weather. As typical
for this time of year, tropical waves are moving through the
tropical Atlantic waters. Of note in the upper levels, the
combination between a mid/upper level trough over the
southeastern United States and an upper level low near 28N69W in
combination with ample moisture and instability over the western
portions is resulting numerous showers and thunderstorms over
the northwest portion of the basin. Scattered showers and
isolated thunderstorms are elsewhere west of 66W. Very stable
conditions under an extensive outbreak of Saharan Air is present
to the east of 66W.

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