[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 091041
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
641 AM EDT Sun Jul 9 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 0600 UTC surface analysis and satellite imagery through
1015 UTC.

...TROPICAL WAVES...

A tropical wave is just offshore the coast of Africa along a
position from near 16N17.5W to 11N18W and to near 06.5N18W. It is
moving westward at about 10 kt. Both water vapor imagery and the
Total Precipitable Water (TPW) imagery animation confirm that deep
tropical moisture continues to increase over and near the
environment of this wave, mainly attributed to it being entrenched
within a very pronounced monsoonal flow that has set up along and
off the coast of W Africa. With this moisture in place, deep
convection near the wave has increased since 24 hours ago.
Scattered moderate to isolated strong convection is within 240 nm
west of the wave from 08N-11N. Scattered moderate isolated strong
convection is within 30 nm of 13N24W.

Another tropical wave is over the far eastern Atlantic with axis
extending from 18N27W to 12N31W to 08N31.5W, moving westward at
10-15 kt. This wave marks the leading edge of deep atmospheric
moisture that has increased between it and the wave just offshore
the coast of Africa. This is clearly evident on latest satellite
imagery, and further supported by the Total Precipitable Water
(TPW) loop animation. The wave has a very good signal at the 700
mb level as indicated in the GFS model guidance. The Meteosat 9
imagery continues to depict an extensive area of African Saharan
dry air and dust to its west. Deep convection directly associated
with this wave is very limited. Only weak isolated showers, at
most, are noted within 90 nm east and 60 nm west of the wave just
north of where it intersects the monsoon trough axis.

A tropical wave, remnants of Tropical Depression Four, is over
the central Atlantic with its axis extending from 24N59W to
19N62W and to 12N63W, and is moving west-northwestward at about
18 kt. The northern portion of the wave is under an upper trough
axis that extends from an upper low (TUTT) located near 29N56W.
The combination of diffluence aloft over this portion of the wave
with the availability of very deep moisture atmospheric
environment surrounding the wave as observed in the TPW loop
animation is supporting a large burst of deep convection
consisting of the scattered moderate isolated strong type
intensity from 20N-25N between 56W-60W. This convection appears to
have been dislodged from the wave and left behind. Scattered
showers and thunderstorms continue to quickly develop ahead of the
wave within 30 nm of a line from 19N62W to along the northern
coast of Puerto Rico. This activity is being detected by the NWS
San Juan radar. The 0052Z Ascat pass from last night revealed
quite an impressive area of 20-25 kt within 90 nm east of the wave
axis from 20N-22N, and within 120 nm west of the wave axis from
20N-23N. The Ascat pass showed a very sharp northeast to southeast
wind shift across the wave axis. The wave is forecast to move
across the Leeward Islands this morning, pass north of Puerto Rico
this afternoon and tonight and move in the general direction of
the SE Bahamas Monday through Tuesday. Expect scattered showers
and thunderstorms with gusty winds to affect mainly the NE
Caribbean today and tonight, with the majority of the activity
shifting west-northwest towards the general vicinity of the SE
Bahamas and that of the northern and eastern portions of
Hispaniola Monday through Tuesday.

A tropical wave is along 75W south of 20N, moving westward at
estimated speed of 19 kt. The latest water vapor imagery shows
subsidence and associated dry air over and around the wave's
environment, except south of 12N where moisture becomes evident.
Scattered moderate convection that developed during the overnight
hours across the Windward Passage is lifting northward towards
eastern Cuba. Scattered strong convection is over Colombia near
the southern extent of the wave. Otherwise, the subsidence and
drier air aloft is allowing for only isolated showers and weak
isolated thunderstorms to exist within 240 nm east of the wave
north of 15N, and isolated showers elsewhere within 240 nm of the
wave.

...ITCZ/MONSOON TROUGH...

The Monsoon Trough axis extends from 11N15W to 10N24W to 08N38W.
The Intertropical Convergence Zone extends from 08N38W to 04N52W.
Aside from the convection related to the tropical waves over the
far eastern Atlantic, scattered strong convection is south of the
axis within 45 nm either side of a line from 04N32W to 05N36W.
Scattered moderate convection is noted within 150 nm south of
the axis between 27W-30W.

...DISCUSSION...

GULF OF MEXICO...

The tropical wave that was over far western portion of the SW
Gulf last night has moved inland Mexico. In the upper levels, a
small upper level high is centered over the western Bay of
Campeche near 19N95W, with the associated anticyclonic flow
covering the western half of the Gulf. An upper level low is noted
just north of NW Cuba, with a trough extending northward to near
28N86W. At the surface, a 1019 mb high is centered over the north-
central Gulf near 27N89W. The associated anticyclonic wind flow
consists of light to gentle winds covers the area north of about
24N. The thermal trough that moved offshore the Yucatan Peninsula
on Saturday evening in combination with upper level anticyclonic
flow and a very moist and unstable air mass in place is initiating
increasing large clusters of scattered moderate to numerous
strong convection over the far SW Gulf, including the western
portion of the Bay of Campeche. An Ascat pass from last night
indicated a tight gradient along the coast of Mexico south of
Tampico as noted by the fresh to strong winds it detected there.
Latest mosaic radar imagery shows scattered showers and isolated
thunderstorms over the extreme SE Gulf and Straits of Florida
moving northwest around 10 kt. Scattered showers and thunderstorms
have developed over the far NE Gulf adjacent to much of the
Florida panhandle ahead of a mid/upper level trough that is over
the eastern United States region. Little change is expected in the
present weather pattern through late Monday.

CARIBBEAN SEA...

A tropical wave is moving across the central Caribbean. See
above for details. A small upper low is near 18N80W, with a
trough extending northwestward to NW Cuba, and another trough
extending southeastward to the coast of NW Colombia. A small
anticyclone is over the eastern Caribbean near 13N65W. The
upper flow between these two features is strong southwesterly,
and is transporting upper debris clouds related to deep convective
activity that is occurring over much of NW Colombia and extreme
northwestern Venezuela. Scattered showers and thunderstorms
between Haiti and eastern Cuba precede the central Caribbean
tropical wave, and are further aided by an upper east to west
trough are just north of Hispaniola. Scattered moderate convection
is developing over the far SW Caribbean south of 11N and west
of 80W. Similar activity is over the waters between Panama and
NW Colombia. The tropical wave along 75W will reach the far
western Caribbean late tonight and move inland central America
early Tuesday. Another tropical wave, currently over the eastern
Caribbean, will track more in a northwesterly motion through
early next week. Saharan dust and drier air will filter in over
the eastern Caribbean behind this wave through Tuesday.

The current pressure gradient supports mainly 10-15 kt trades
throughout, except for stronger winds of 20-25 kt are near the
coast of Colombia. Little change is expected with this gradient
into Tuesday.

...HISPANIOLA...

Scattered showers and thunderstorms over the Windward are
ahead of the tropical wave along 75W as discussed above. An
upper level cyclonic shear axis extending east to west over the
vicinity of the island in addition to deep atmospheric moisture
in the wake of the tropical wave will maintain scattered showers
and isolated thunderstorms over the waters just to the south of
Hispaniola, with some of this activity expected to impact the
eastern and southern portions of the island through Monday.
Also, expect the typical diurnal scattered shower and thunderstorm
activity to occur over some of the interior sections of Hispaniola
through early next week.

ATLANTIC OCEAN...

Three tropical waves are analyzed over the tropical Atlantic. See
above for details. A nearly stationary high pressure of 1030 mb
is centered well north of the area at 36N42W, with a ridge
stretching southwestward to 32N55W and to central Florida. An
upper level low (TUTT) is observed to be near 29N56W, with a
trough reaching south to 23N55W, then west-southwest as a cyclonic
shear axis to 21N68W and to 21N77W. Scattered showers and
thunderstorms are within 90 nm of the low in the northeast
quadrant. Isolated showers and thunderstorms are elsewhere north
of 25N between 51W and 58W. Isolated showers are north of 27N
between 58W and 63W. Scattered showers and isolated thunderstorms
moving west-northwest are over much of the western half of the
area, except for a pocket of scattered showers and thunderstorms
observed between the central and SE Bahamas and Cuba. The
aforementioned ridge will begin to lift northward on Monday.
Expect for the shower and thunderstorm activity over the
western part of the area to continue into early next week as
atmospheric conditions remain moist and unstable, and a mid/upper
level trough over the eastern United States moves little. An
extensive area of African Saharan dust is situated over the
eastern and central Atlantic E of 57W, and is gradually migrating
westward.

For additional information please visit
http://www.hurricanes.gov/marine

$$
Aguirre
This weather bulletin was brought to you by:
www.nashvilleweather.net