Atlantic Tropical Weather Discussion (Text)

AXNT20 KNHC 270003

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
805 PM EDT Mon Jun 26 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 
2315 UTC.


A tropical wave axis is along 26W from 01N to 11N, moving 
westward at 15 kt. The wave is embedded within a rather moist 
environment, however Saharan dry air and dust is intruding some 
around the northern segment of the wave s surface ridging noses 
south just to the west of the wave. Only widely scattered 
moderate to isolated moderate convection is present within 120 
nm either side of the axis from 07N to 10N. This activity 
appears to be on the decreasing trend.

A broad tropical wave with axis is along 46W from 01N to 11N, 
moving westward at 10-15 kt. The wave is in a region of 
favorable wind shear. It is also within a moderate moist 
environment and under an area of diffluent flow aloft that is 
located between an upper anticyclone near 15N51W and mid/upper 
ridging to the southeast of the wave. In addition 700 mb 
streamline analysis also supports a wave signal near that of the 
surface position. Scattered moderate isolated strong convection 
is seen within 180 nm east of the axis from 06N-08N, within 180 
nm west of the axis from 10N-11N and within 60 nm west of the 
wave from 07N-08N. 

A tropical wave is over the central Caribbean axis along 69W/70W 
south of 19N to inland Venezuela near 08N69W, moving westward at 
15-20 kt. The wave is in a region of unfavorable wind shear and 
in a limited moist environment. Deep convection that develops 
near and along the wave axis is observed to have a short 
duration due to the moderate to strong westerly winds aloft. 
Scattered moderate isolated strong convection is seen within
30 nm of a line from 17N71W to 17.5N74W. Scattered showers and 
isolated weak thunderstorms are elsewhere within 120 nm west
of the axis from 14N-17N. Isolated showers are within 60 nm 
east of the wave axis.

A tropical wave is over the western Caribbean with axis along 
86W south of 21N to the northwest section of Costa Rica, moving 
westward at about 15 kt. The southern portion of the wave is 
very near the eastern Pacific monsoon trough that extends across 
the SW Caribbean Sea. The wave marks the leading edge of deep 
tropical moisture that trails the wave east to near 78W. 
Clusters of scattered moderate isolated strong convection are 
located within this area of deep moisture south of 17N to inland 
northern Honduras between the wave axis and 83W, and also south 
of 16N between 77W and the coast of central America. The 
activity south of 16N between 77W and the coast of central 
America is mainly associated with the monsoon trough. This wave 
is forecast to move inland early on Tuesday.


The Monsoon Trough axis extends from the coast of Africa near 
15N17W southwest to near 05.5N25W. The Intertropical Convergence 
Zone axis then begins just to the west of the tropical wave 
along 26W near 05N28W, and continues to 06N37W to 05N45W. 
05N52W. Scattered moderate isolated strong convection is within 
180 nm south and 60 nm north of the axis between 41W-43W.



A broad upper level trough extends from over the eastern United 
States seaboard southwest to the extreme northeast portion of 
the Gulf, then becomes a narrow trough south to near 24N85W. 
This feature supports a stationary front that is analyzed from 
just offshore NE Florida southwest to Cross City and to 29N86W, 
and northwest from there to inland southeastern Louisiana.
Widely scattered showers and isolated thunderstorms are noted 
along, and within 60 nm south of the boundary west of 88W. 
Isolated showers are elsewhere within 30 nm of the boundary.
The boundary is forecast to gradually become diffuse through 
Tuesday afternoon, with the remnants possibly lifting back north 
as a warm front. The portion of the front along the Florida 
coast may sag some to the south through Tuesday as high pressure 
to its north builds in from the northwest.

Upper level anticyclonic wind flow covers the rest of the Gulf 
of Mexico, especially from the area of the upper level trough, 
southwestward to over SW portion of the area. A pair of surface 
troughs are analyzed over the SW and far western portions of the 
Gulf. One surface trough extends from just east of southern 
Texas to 21N96W and southeast to near 18N94W. Scattered showers 
and isolated thunderstorms are noted within 90 nm east of the 
trough south of 23N, while isolated showers are within 60 nm to 
its west south of 23N. The second surface trough extends along 
93W from 20N-26N. Scattered moderate isolated strong convection 
is within 120 nm east of this trough from 22N-24N, and also 
within 60 nm west of the trough from 21N-23N. A weak pressure 
pattern is present elsewhere.


The main features in the basin are two tropical waves already 
discussed in the waves section above. Aside from the shower and 
thunderstorm activity associated with them as described above, 
latest scatterometer data depicts fresh to strong winds in the 
vicinity of the waves south of about 17N. These winds are 
expected to increase to near gale across the Gulf of Venezuela 
on Tuesday night. Otherwise, scattered showers and thunderstorms 
are developing over the Windward Passage and just north of 
Jamaica. Isolated showers in streamer fashion are observed over 
the eastern Caribbean, and over portion of the northwest 
Caribbean north of the shower and thunderstorm activity 
associated with the tropical wave along 86W. A broad tropical
wave currently over the central tropical Atlantic is expected to 
enter the eastern Caribbean Sea on Tuesday night, and reach the 
central Caribbean late on Wednesday. This wave will be 
accompanied by scattered showers and thunderstorms, some of 
which may contain gusty winds.


Upper level moderate to strong southwest to west winds continue 
to advect deep level moisture over Hispaniola and surrounding 
waters as the northern portion of a tropical wave moves across 
the far eastern part of the island this evening. With these 
factors in play and in addition to the presence of ample 
instability as well, expect scattered showers and thunderstorms 
to be on the increase over much of the island through the next 
day or so.


Surface high pressure covers the basin, with the parent 1025 mb 
anticyclonic center located just north of the area at 33N47W.
A broad upper trough along the United Stated eastern seaboard 
supports a stationary front that extends from a 1016 mb low 
pressure center near 32N79W southwest to inland NE Florida. A 
short-wave trough riding along the southern periphery of the 
upper trough in combination with the surface boundary is 
activating increasing clusters of scattered moderate isolated 
strong convection over the far northwest portion of the basin to 
inland NE Florida. This activity is expected to continue quite 
active through late Tuesday as the surface boundary begins to 
drift southward, and upper level dynamics provide further 
support to maintain it active.

A large upper level cyclonic circulation is situated over 
the central Atlantic 28N57W, and is slowly moving northwestward.
Isolated showers and thunderstorms are noted north of 24N 
between 52W-63W. Similar activity is to its west within 30 nm of 
a line from 28N66W to 32N69W. Another upper level cyclonic is 
moving south-southwest over the eastern portion of the basin 
near 28N26W. Isolated showers and thunderstorms are possible 
within 120 nm of the southeast quadrant of the low. Otherwise,
isolated showers and thunderstorms are evident elsewhere west of 
about 50W. They are moving in a general westward motion. Stable 
and rather stable atmospheric conditions are present to the east 
of 50W under stronger high pressure.

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Page last modified: Tuesday, 27-Jun-2017 00:03:38 UTC