Tropical Weather Discussion
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AXNT20 KNHC 280005

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
805 PM EDT Tue Jun 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 1800 UTC surface analysis and satellite imagery through
2315 UTC.


A tropical wave has its axis just off the Africa coast along 18W
from 10N to 20N, moving westward near 10 kt. While there is
moisture aloft in the form of broken high clouds, low-level
moisture noted earlier with this wave has become limited north of
16N during the afternoon. Only isolated showers and weak
thunderstorms are within 180 nm west and 60 nm east of the wave

A tropical wave has its axis along 33W/34W from 02N to 11N,
moving westward at 10-15 kt. Last visible satellite imagery and
Total Precipitable water (TPW) data reveals that the wave remains
embedded within a very moist and unstable environment, except for
over its extreme northern segment where Saharan dry air and dust
is present. The latest satellite imagery shows scattered moderate
to isolated strong convection ahead of the wave within 30 nm of a
line from 10N33W to 08.5N35W. Small clusters of scattered moderate
convection are elsewhere within 180 nm west of the wave axis from
06N to 10N. A few small clusters of scattered moderate convection
are in the wake of the wave from 08N-11N.

A broad and rather robust tropical wave has its axis tilted in a
northeast to southwest fashion along a position from 14.5N54W to
11N58W to inland South America at 07N59W, moving westward 15-20
kt. This wave continues to be easily identifiable on visible
satellite imagery as having the typical configuration of waves
observed later during the season. It is detected in the model
fields, and is further supported by the latest diagnostic model
analysis. Scattered moderate isolated strong convection is ahead
of the wave axis within 60 nm of a line from 12N57W to 11N59W, and
within 45 nm of a line from 11N59W to 10N6.5W. Scattered moderate
convection is within 30 nm of a line from 13N55W to 12N57W. In
the wake of the wave, scattered moderate convection is within 30
nm of 11N52W. The wave is forecast to begin to enter the
southeastern Caribbean Sea late tonight into early Wednesday,
then move across the rest of the eastern Caribbean through
Wednesday night, and the central Caribbean portion Thursday. The
wave will be accompanied by scattered showers and thunderstorms
with gusty winds, and followed with some area of haze.

A tropical wave is moving into the western Caribbean Sea with its
axis along 80W/81W south of 21N to across northern Panama, moving
westward at 10-15 kt. This wave is also evident in visible
satellite imagery, and continues to mark the leading surge of very
deep atmospheric moisture as seen in Total Precipitable water
(TPW) data and in the satellite imagery. An area of scattered
moderate to isolated strong convection is east of the wave axis
to 77W and from 14N to 18N. Similar activity is within 30 nm of
12N78W. Scattered showers and isolated thunderstorms are west of
the wave from 11N to 15N. The wave will move across the remainder
of the western Caribbean Sea through Wednesday, and inland Central
America Wednesday night.

A tropical wave is just west of the Yucatan Peninsula near 91W
and south of 22N, and extends southward to inland southeastern
Mexico, moving westward around 10 kt. The wave has contributed to
the typical diurnal convection that occurs over the Yucatan
peninsula. Increasing clusters of scattered strong convection
are noted over much of the interior of the Yucatan peninsula
as well as the northern portion of Guatemala. This activity is
beginning to spread into the far eastern section of Mexico.
This wave will most likely become ill-defined over the SW Gulf on
Wednesday, however the southern extent of the wave is expected
to continue on westward over the eastern Pacific Ocean.


The Monsoon Trough axis extends from the coast of Africa near
20N17W, and continues southwest to 10N25W and to 07N32W. The
Intertropical Convergence Zone then extends from just to the
west of the tropical wave along 33W/34W northwest to 09N44W to
09N50W and to just east of the tropical wave along the position
of 14.5N54W to 11.5N58W to 07N59W. Scattered moderate isolated
strong convection is within 180 nm south of the ITCZ axis between
50W-53W. Similar activity is within 30 nm of 05N48W. Scattered
moderate convection is within 120 nm south of the ITCZ axis
between 37W-39W, and within 30 nm of 05N42W.



A mid to upper level trough axis is over the far NW Gulf, while
a surface trough is along the Texas coast. The combination of
these features along with the presence of diffluent flow aloft
east of the mid-upper level trough continues to support scattered
showers and thunderstorms from 24N to 27N and west of 89W, and
scattered showers and isolated thunderstorms north of 27N west
of 88W. A stationary front is analyzed from NE Florida southwest
to near Cross City, Florida and to 29N86W where it becomes diffuse
from there to just east of southeastern Louisiana. Weak high
pressure is analyzed over the remainder of the Gulf. The shower
and thunderstorm activity over the western Gulf is forecast to
remain active tonight and Wednesday, then shift ENE Wednesday
night and Thursday as the mid/upper level trough slides eastward.
The stationary frontal boundary is forecast to gradually become
diffuse through early Wednesday, with the remnants lifting back
to the north later on Wednesday and through Wednesday night.
A tropical wave is over the eastern Bay of Campeche. Associated
convection is described above under Tropical Waves.


The main feature presently in the basin is the tropical wave
discussed in the section above, and the near future arrival of
another tropical wave also discussed above expected to move
into the southeastern Caribbean late tonight into early Wednesday,
and move across the central Caribbean Thursday. Otherwise, a
pressure gradient is analyzed throughout the basin. The southern
extension of a central Atlantic mid to upper level trough
passes from east to west just to the north of eastern Cuba
and Hispaniola, and is helping to produce scattered showers and
isolated thunderstorms over the waters between eastern Cuba and
Jamaica, and over the Windward Passage. Some of the moisture with
this activity is related to the tropical wave along 80W/81W, and
is also moisture that is being advected towards Hispaniola by
upper level westerly winds as mentioned below. The gradient is
forecast to tighten over portions of the far south-central
Caribbean beginning tonight and continuing through Thursday night
inducing strong to near gale force east winds there, with the near
gale force winds expected across and near Gulf of Venezuela.
Scattered low clouds with possible isolated showers are present
over the eastern half of the sea, with the exception of the far
southeast sector where mid and high level clouds are increasing
from the east in advance of the tropical wave that is approaching
the Caribbean. In addition, scattered showers and thunderstorms,
some with gusty winds, that are preceding the aforementioned
tropical wave are observed just to the east and southeast of the
Windward Islands. This activity will move across these islands and
the southeastern Caribbean tonight into Wednesday.


Upper-level westerly winds continue to usher deep-level moisture
over the island and surrounding waters this evening. This is
contributing to the shower and thunderstorm activity that
developed this afternoon to bring about a further increase to
this activity. Little change is expected in the present weather
pattern through Wednesday, then a gradual decrease in moisture
through Thursday night as a strong tropical wave passes to the
south of the island.


Broad anticyclonic aloft covers the Atlantic west of about 65W.
A broad mid to upper trough extends southwestward from along the
eastern seaboard to the far northwest portion of the basin. It
supports a stationary front extends through 32N79W to just south
of Saint Augustine, Florida as of 21Z.  Scattered showers and
thunderstorms are noted over much of the northwest portion north
of the Bahamas and west of about 74W. This activity will continue
through much of Wednesday and Wednesday evening as the surface
boundary weakens, and the mid to upper trough slides eastward
while it broadens out further. Surface high pressure is analyzed
north of 18N between 20W and 70W, and weakens to the west of 70W.

A large and well-defined mid to upper level cyclonic circulation
is located over the central Atlantic near 28N56W and is nearly
stationary, with an associated trough stretching from it southwest
to 22N64W to 21N72W and to across the NW Caribbean Sea. The
circulation covers the area north of 23N and between 49W and 62W.
It is forecast to drift northward and gradually weaken to a
trough through Wednesday night. Over the far eastern Atlantic,
another mid to upper level cyclonic circulation is centered near
29N30W. It is moving westward. Only isolated showers and possible
weak isolated thunderstorms are within 180 nm in the southeast
quadrant of the circulation center. A trough extends from the
circulation south-southwest to near 11N39W.

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