AXNT20 KNHC 270605
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
205 AM EDT Thu Jul 27 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 0000 UTC surface analysis and satellite imagery through
An eastern Atlantic tropical wave has its axis extending from
17N29W to 12N29W to 04N29W is moving westward at an estimated
motion of about 10 kt. A low to mid-level cyclonic circulation is
noted just west of the wave near 11N30W and is supported by 700
mb troughing over it and across the wave north of 10N. However,
the METEOSAT-9 imagery shows abundant dense Saharan dry air and
dust across the wave north of 13N. Latest satellite imagery shows
scattered strong convection developing on the wave axis within 30
nm of 11N29W, and just west of the wave within 30 nm 11N30W.
Isolated showers are elsewhere within 120 nm either side of the
wave south of 13N.
A central Atlantic tropical wave has its axis extending from
16N38W to 11N39W to 03N38W, moving westward at 10-15 kt. This
wave is moving through a very stable region of the Atlantic where
deep moisture is being suppressed as was evident in the last
visible imagery from Wednesday, and as currently seen in the
METEOSAT-9 imagery. The METEOSAT-9 imagery displays abundant
Saharan dry and dust over and northwest through northeast of this
wave. The CIMSS total precipitable water (TPW) imagery animation
shows moisture in relation to this wave confined to south of 11N
near and along the location of the monsoon trough. Latest
satellite imagery shows scattered moderate isolated strong
convection within 240 nm east of the wave axis along and north of
the monsoon trough from 08N-10N. Scattered moderate convection is
west of the wave within 30 nm of 08N41W. Scattered showers and
isolated thunderstorms are elsewhere within 180 nm west of the
wave from 06N-11N.
A tropical wave approaching the Lesser Antilles is along 57W from
11N-24N, moving westward at 15 kt. This wave continues to exhibit
a pretty well-defined cloud pattern on latest satellite imagery.
The GFS 700 mb guidance indicates broad troughing over the
vicinity of this wave. Similar troughing signature is also
noted at 850 mb. Both latest satellite imagery and the TPW
imagery animation depict a swath of moisture along and within
120 nm either side of the wave axis from 13N-24N and a larger
area of deeper moisture south of 13N within 240 nm east and
180 nm west of the wave axis. Scattered showers and thunderstorms
are occurring within these moisture areas. The wave is forecast
to move across the Lesser Antilles and into the far eastern
Caribbean Sea today, and move across the rest of the eastern
Caribbean Sea though Friday night, then through the central
Caribbean Saturday and Saturday night. Scattered showers and
isolated thunderstorms are possible with this wave.
An eastern Caribbean Sea tropical wave is along 70W south of 19N,
moving westward at 15 kt. Relatively drier air east of the wave
north of mainly 15N is allowing for only isolated showers and
thunderstorms to exist to the east of this wave, with a little
in the way of more shower and thunderstorm over the far eastern
portion of the Caribbean Sea. Similar activity is within 60-90 nm
west of the wave. This wave will move across the rest of the
Caribbean through tonight, and across the western Caribbean Sea
Friday through Saturday.
The monsoon trough axis extends from 13N17W to 11N29W to 07N39W
to 07N45w, where scatterometer winds indicate the ITCZ begins
and extends to near 07N43W and continues to 09N61W. Aside the
convection mentioned in the tropical wave section, scattered
moderate isolated strong convection is within 120 nm north of
the monsoon trough between 32W-34W, and within 30 nm, of the
monsoon trough between 51W-54W. Scattered moderate convection
is within 60 nm south of the monsoon trough between 34W-38W.
GULF OF MEXICO...
In the upper levels, a small upper level low is over the NW Gulf
at 28N95W, with a trough extending southward to the SW Gulf. A
mid-upper level trough is along the far northern coastal sections
of the Gulf. Plenty of deep moisture and instability is present
throughout the area. At the surface, a 1018 mb high is centered
over the north central Gulf of Mexico near 28N91W. The associated
anticyclonic flow consists of gentle to moderate winds across
the basin. A surface trough is over the W Gulf of Mexico from
24N97W to 19N95W. Scattered moderate convection is moving offshore
the central Florida peninsula from 25N-28N. Scattered showers and
isolated thunderstorms are over much of the western Gulf south of
27N west of 90W, while isolated showers and thunderstorms are
south of 25N east of 90W. Little change is expected through
Saturday for the majority of the Gulf. On Saturday, a weak front
is forecast to drop south over the southeastern United States to
near the Florida panhandle by late Saturday may bring an increase
of moisture along with shower and thunderstorm activity to the NE
Gulf at that time.
A tropical wave is moving across the central Caribbean. See above
for a discussion on this feature that includes associated shower
and thunderstorm activity. Scattered showers and isolated
thunderstorms are over the western Caribbean from 12N- 18N west of
79W, whiles isolated showers and thunderstorms are elsewhere over
the central and western Caribbean waters. Elsewhere, the
eastern extension of the Pacific monsoon trough in combination
with additional instability provided by an upper level low near
12N81W is expected to set-off scattered to numerous showers and
thunderstorms over the SW Caribbean Sea later this morning. The
pressure gradient throughout supports 15-25 kt trade winds across
the sea, with the strongest winds over the central Caribbean.
The current observed will have little changes through the next
24-48 hours, with the exception of expected impacts by the
tropical waves described above.
Scattered moderate convection is dissipating over Haiti early
this morning. With a tropical wave along 70W, expect some increase
in moisture across the island through today. This in combination
with daytime heating and local effects should lead to the
development of scattered moderate to strong convection over some
areas of the island. This activity should last into tonight.
Moisture is expected to decrease on Friday and Friday and
increase on Saturday as another tropical wave passes through the
central Caribbean Sea.
In the upper levels, a large and elongated upper level low is
centered over the western Atlantic near 28N57W, with a trough
stretching southwestward to the NE Caribbean Sea and westward to
Hispaniola. Scattered moderate convection is noted from 25N-29N
between 53W-56W. Similar activity is north of 30N west of 79W.
Scattered showers and isolated thunderstorms are seen west of
66W. In the tropics, there are three tropical waves. See above
for discussions on these features. Elsewhere at the surface, a
1024 mb high is centered over the central Atlantic near 31N45W,
with a ridge extending southwestward to central Florida. Outside
the aforementioned observed convection, the high pressure is
maintaining rather stable and dry conditions throughout. The
METEOSAT-9 satellite imagery shows abundant Saharan dry and dust
present over the eastern Atlantic and over much of the central
Atlantic. Some broken areas of dust are over the western Atlantic.
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