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870
AXNT20 KNHC 151804
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
204 PM EDT Sun Jul 15 2018

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 1200 UTC surface analysis and satellite imagery through 1745 UTC.


...SPECIAL FEATURES...

Subtropical Storm Beryl is centered near 30.1N 64.7W at 15/1500 UTC or about 350 nm N of Bermuda, moving ENE or 75 degrees at 3 kt. The estimated minimum central pressure is 1010 mb. Maximum sustained wind speed is 35 kt with gusts to 45 knots. Latest satellite imagery shows that Beryl has weakened since yesterday as noted by its exposed center that consists of broken to scattered low to mid-level clouds. Since it is a sheared cyclone, the remaining scattered moderate convective activity is displaced within 90 nm to the SE of its center. Per the 15Z NHC advisory Beryl is forecast to resume a northeastward track motion by tonight, with a faster northeastward motion Mon and Tue. Beryl is forecast to maintain intensity through this evening, before it begins to quickly weaken to a depression and dissipate by Wed. Isolated moderate rainshowers are from 22N to 31N between 70W and 80W. Please read the latest NHC Forecast/Advisory under AWIPS/WMO headers MIATCMAT2/WTNT22 KNHC and high seas forecasts issued by the National Weather Service under AWIPS header NFDHSFAT1 and WMO header FZNT01 for more information.

SW Caribbean Sea gale warning: NE to E minimal gale force winds near the coast of Colombia diminished to near gale force shortly after 12Z this morning. The presence of strong central Atlantic high pressure in place, with the additional factors of a series of tropical waves continuing to pass through the Caribbean Sea along with the typical broad area of low pressure present over the SW Caribbean Sea and the northwestern section of S America will continue to be a very favorable synoptic pattern set-up for similar gale force winds to return to the coastal waters of Colombia for tonight, Tue night, and Wed night. Resultant seas with these winds are forecast to be in the range of 9-14 ft, with the highest of this range expected near 12N76W. Please read the High Seas Forecast, under the AWIPS/WMO headers HSFAT2/FZNT02 KNHC, for more details.


...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis along 29W/30W from 07N to 18N, with a 1012 mb low analyzed on the southern part of its axis near 09N30W moving westward at 10-15 kt. The wave is depicted on GOES-16 RGB imagery as having a rather broad envelope of broken to overcast mainly stratocumulus clouds covering the area from 10N- 19N between 30W-40W. It remains in a low to moderate deep layer wind shear environment. Scattered moderate convection near this system is primarily related to the monsoon trough as described below under Monsoon Trough/ITCZ. The GOES-16 RGB images along with visible images of the far eastern Atlantic are depicting yet another massive plume of Saharan dry air and associated dust following in behind the wave from 10N- 28N. Visibility within this area of dust is being reduced quite significantly.

A central Atlantic tropical wave has its axis extending from near 20N57W to 13N60W and to inland northeastern Venezuela at 08N61W, moving westward at 15-20 kt. This wave continues to be impacted by Saharan dust, which is not allowing for any deep convection to develop along and near it. Only isolated showers moving quickly westward with the fresh easterly trades are seen within about 300 nm east and 180 west of the wave axis. This wave will move across the eastern Caribbean Sea through Tue night, and the central Caribbean Wed through Thu. As the wave approaches from 65W to 70W, it may be able to initiate scattered showers and isolated thunderstorms as it approaches the eastern section of an upper level trough that is currently anchored from near eastern Cuba to the vicinity of Jamaica and to near 10N80W.

A central Caribbean Sea tropical wave axis is along 76W S of 20N to the Colombian/Panamanian border, moving westward around 15 kt. This wave is ill-defined at the surface. Its position was based on extrapolation from the past 6 to 24 hr analyzed position and from the latest guidance from 700 mb model diagnostics. No deep convection is noted with this wave as it located to the west of an upper level trough as mentioned in the above paragraph. Similarly to the previous wave, only isolated showers moving quickly westward with the fresh easterly trades are noted near the wave.

The former western Caribbean Sea tropical wave has moved inland Central America, with is axis near 83W. The northern part of the wave reaches to near 17N. It is moving westward at 10-15 kt. The combination of this wave with local topography effects has initiated scattered to numerous showers and thunderstorms over much of the central and southern sections of Nicaragua, including its immediate coastal waters as well as those of Costa Rica. Scattered showers and thunderstorms are seen over the northeastern section of Nicaragua and the eastern section of Honduras. Model guidance indicates that 700 mb troughing is present over much of Central America providing further support for the shower and thunderstorm activity. The wave will move into the eastern Pacific Ocean on Mon, with its northern segment possibly enhancing shower and thunderstorm activity over El Salvador and the southern section of Honduras.


...MONSOON TROUGH/ITCZ...

The monsoon trough axis stretches from well inland Africa to through the coastal sections of Guinea-Bissau to 10N25W to the 1012 mb low that is on the eastern Atlantic tropical wave along 29W/30W, and continues to 07N36W, where latest scatterometer data indicates the ITCZ begins and continues to 05N40W to 06N50W. Scattered moderate convection is within 120 nm north of the ITCZ between 37W-45W and within 90 nm south of the trough between 30W-33W. Other scattered moderate convection is south of the ITCZ within 30 nm of a line from 03N39W to 04N44W to 04N52W.


...DISCUSSION...

GULF OF MEXICO...

High pressure of 1019 mb as of 15Z is the main feature that is influencing the synoptic pattern across the basin. Its associated gradient is allowing for generally light to moderate anticyclonic flow to exist over the gulf waters. Current NWS mosaic radar displays show scattered showers and isolated thunderstorms over much of the eastern gulf waters as well as over the eastern half of the central gulf. This activity is moving westward under moderate upper northeast winds. The activity should continue into the early evening, with some possibility of more activity developing during the overnight hours.

The high pressure will prevail across the northern waters through Thu. A surface trough will move westward off the Yucatan Peninsula each evening through Thu, enhancing nocturnal winds in the SW Gulf.

CARIBBEAN SEA...

Please read the Special Features section for details about the pulsing gale-force winds near the coast of Colombia.

Aside from the tropical wave features as described above, an upper level trough is noted on water vapor imagery to be anchored from near eastern Cuba to vicinity Jamaica and to near 10N80W. Scattered to broken high clouds streaming northeastward are seen within 600 nm to its southeast. Isolated showers moving rapidly to the west are present over much of the basin, except along the immediate coasts of Central America S of 16N where deeper convective activity is occurring as described above with the inland tropical wave along 83W. This activity should persist through Mon night or so. Otherwise, a tight pressure gradient will allow for NE-E winds to pulse to minimal gale near the coast of Colombia over the next few days as described above under Special Features. Fresh to strong E winds will continue over the central Caribbean Sea through the middle of next week.

ATLANTIC OCEAN...

Please read the Special Features section for details about Subtropical Storm Beryl.

A weak 1018 mb was analyzed near 31N78W as of 15Z with a trough extending southwestward to near Cape Canaveral, Florida. Recent scatterometer data picked up on this feature. Current NWS mosaic radar imagery along with recent satellite imagery show increasing scattered moderate isolated strong convection within 90 nm of the low in the SE and S quadrants. Another surface trough is analyzed from near 32N64W to 29N68W to 28N72W to the NW Bahamas. This trough is being supported by an upper-level trough providing ample forcing to allow for scattered moderate isolated strong convection to be present within 300 nm SE of the trough, except within 120 nm SE and S of the trough between 65W-70W. The second surface trough will slowly weaken through Tue as the upper trough lifts to the NE away from it. High pressure will build in the wake of the trough. Scattered showers and isolated thunderstorms between the Bahamas and southeastern Florida are due to a weak surface.

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

$$ Aguirre

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