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000
AXNT20 KNHC 280837 CCA
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
205 AM EDT Fri Jul 28 2017

corrected surface analysis time

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 0545 UTC.


...TROPICAL WAVES...

An eastern Atlantic tropical wave extends its axis from 19N34W to broad low pressure of 1012 mb at 10N34W and to 06N34W, moving westward at 10 kt. Scattered moderate convection is noted from 09N-12N between 32W-38W. Both satellite imagery and the total precipitable water (TPW) imagery animation both reveal that moisture has increased within the surrounding environment of the this system, and seems to have overtaken most of the Saharan dust that has been present over its northern portion the past several days. Scattered moderate isolated strong convection is seen within 45 nm of 12N34W. Scattered moderate convection is within 30 nm of line from 12N34W to 11N37W.

A central Atlantic tropical wave extends its axis from 19N43W to 12N45W to 03N45W, moving west at 10 to 15 kt. This wave is moving through a very stable atmospheric environment marked by the presence of a very pronounced African Saharan Air Layer that covers the eastern and central Atlantic north of the tropics. Latest water vapor imagery confirms that strong subsidence and resultant dry air prevails over the the northern and central portions of this wave. The total precipitable water (TPW) imagery animation shows that moisture associated with this wave is suppressed to the south of 12N within the region where the monsoon trough transitions to the ITCZ. Satellite imagery shows scattered moderate isolated strong convection west of the wave within 30 nm of a line from 08N46W to 09N47W. Scattered moderate convection is east of the wave to 43W from 05N-09N. The wave is forecast to approach the Lesser Antilles late on Sunday.

An eastern Caribbean tropical wave is near 63W, and extends northward to the Atlantic near 21N. Water vapor imagery depicts dry subsident air over the wave north of 15N. No deep convection is occurring with this wave. Only isolated showers and weak isolated thunderstorms moving quickly westward in the trade wind flow are noted within 150 nm either side of the wave. This wave will move across the remainder of the eastern Caribbean through tonight, then through the central Caribbean on Saturday.

A central Caribbean tropical wave is just east of Jamaica with its axis along 76W south of 18.5N. It is moving west at about 17 kt. Moisture with this wave remains rather shallow at the low-mid levels to its, while at the upper levels water vapor imagery shows a thin moisture in the form of scattered high clouds streaming eastward across the wave. The southern portion of the wave is aiding strong type convective complex observed over northwestern Colombia and its adjacent waters. Otherwise, only isolated showers and thunderstorms moving quickly westward in the trade wind flow are within 120 nm east and 300 nm west of the wave north from 14N-18N. The wave will move across the rest of the central Caribbean through most of this morning, then across the western Caribbean through tonight and inland central America on Saturday.


...ITCZ/MONSOON TROUGH...

The monsoon trough axis extends from 19N16W southwest to 13N24W to a 1012 mb low at 10N34W and to 07N45W, where scatterometer data indicates the ITCZ then begins and continues to 07N50W to near 06N56W. Aside from convection related to the tropical waves as described above, scattered moderate isolated strong convection is within 60 nm south of the monsoon trough between 38W-40W, and also to the south of the monsoon trough from 06N-09N between 26W-30W. Scattered moderate convection is within 180 nm south of the trough between 40W-43W.

Scattered moderate isolated strong convection is south of the monsoon trough from 06N-09N. Scattered moderate convection is well to the southeast of the monsoon trough off the coast of Africa from 05N-09N between 14W-19W.


...DISCUSSION...

GULF OF MEXICO...

In the upper levels, a small upper low moving west is over the north-central Gulf at 27N91W. The southern periphery of strong riding aloft associated with a large anticyclone over Oklahoma covers the northern portion of the Gulf. Dry air aloft is present over some areas of the central and western Gulf. At the surface, a weak 1016 mb high is centered over the NW Gulf at 28N92W. It is maintaining a rather weak pressure pattern over the area. A 1014 mb low is over northern Florida near 30N84W with a trough extending southwest to 27N88W. Latest satellite imagery and NWS mosaic radar animation are indicating less shower and thunderstorm activity over the basin than what was seen the past few nights. Scattered showers and isolated thunderstorms are mainly over the far SE Gulf and Straits of Florida, and are moving to the west. Isolated showers and thunderstorms are over the NE Gulf near the surface trough, and also from 26N-28N east of 87W.

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 an increase in shower and thunderstorm activity to the NE Gulf at that time.

CARIBBEAN SEA...

Two tropical waves are moving across the basin. Refer to the section above for details on these features. Scattered showers and isolated thunderstorms continue over the western Caribbean elsewhere to the west of the activity associated with the tropical wave along 76W. This activity is located on the southern periphery of an upper-level low centered just south of western Cuba as seen in water vapor imagery. Scattered moderate isolated strong convection has quickly developed over the SW Caribbean from 09N-13N west of 80W. Isolated showers and possible isolated thunderstorms are elsewhere over the western Caribbean. The present pressure gradient will allow for fresh to strong trades to continue over the south-central Caribbean through the weekend, with moderate to locally fresh trades elsewhere.


...HISPANIOLA...

The scattered showers showers and thunderstorms that developed over the interior portions of the island on Thursday have dissipated. Only isolated showers and thunderstorms are noted over some of the interior locations of the island as well as over its adjacent waters. Scattered showers and thunderstorms are expected to develop again today with daytime heating and local effects in play over some of the interior locations. With dry air aloft nearby, this may limit the activity some. Moisture should increase on Saturday as the present eastern Caribbean tropical wave passes through the central Caribbean.

ATLANTIC OCEAN...

In the upper levels, a large upper-level low lifting northward is identified to be near 26N58W, with a trough stretching south- southwestward to 21N59W and to the northeastern portion of the Caribbean. This low is reflected at the surface as a trough that extends along a position from 31N56W to 23N59W. Isolated showers and thunderstorms are seen north of 22N between 53W-62W. Scattered showers and thunderstorms are north of 28N between 63W-70W, and are ahead of a stationary front north of the area. Scattered showers and isolated thunderstorms are over and near the Bahamas. Otherwise, higher surface ridging along 28N is supporting light to gentle breezes and slight seas. Farther east, high pressure over the central Atlantic is maintaining gentle to moderate trade winds, with Saharan dust dominating east of 55W and is resulting in very stable conditions there.

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

$$ Aguirre

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