541 AXNT20 KNHC 171204 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 804 AM EDT Tue Jul 17 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 0600 UTC surface analysis and satellite imagery through 1145 UTC. ...SPECIAL FEATURES... SW Caribbean Sea gale warning: The pressure gradient is forecast to tighten between strong central Atlantic high pressures and broad low pressure over the southwestern Caribbean Sea beginning late Wed night increasing the present ongoing strong NE-E winds over the area from 11N-15N between 70W-77W, including the waters along the coast of Colombia, to increase to minimal gale force. These winds will weaken to just below gale force in the early morning hours of Thu. Seas are expected to build to the range of 10-14 ft with the gale force winds, then subside to 8-11 ft Thu morning. Please read the High Seas Forecast, under the AWIPS/WMO headers HSFAT2/FZNT02 KNHC, for more details. ...TROPICAL WAVES... A tropical wave was identified yesterday to be moving through western Atlantic, and as of 0600 UTC this morning it was analyzed along 15W from 03N-16N, moving W at 15 kt. A well defined 700 mb trough is noted together with an inverted-V pattern in its associated cloud/convection structure. Scattered moderate isolated strong convection is ahead of the wave from 08N-12N between 17W- 20W. Saharan dust is noted on GOES-16 imagery behind and around this tropical wave. A central Atlantic tropical wave extends from near 20N45W to 14N47W to 06N48W, moving westward at 15-20 kt. The wave is depicted on GOES-16 RGB imagery as having a rather broad inverted-V shape envelope of broken to overcast stratocumulus clouds from 09N-22N between 38W- 53W. Scattered moderate convection is seen within 120 nm to the west of the wave from 14N-17N, and within 180 nm east of the wave from 06N-07N. Scattered showers and isolated thunderstorms are within 180 nm to the west of the wave from 10N-14N. The GOES-16 RGB 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 09N-27N east of 36W to well inland of W Africa. A tropical wave axis over the central Caribbean extends from just west of Haiti to 15N75W to inland NW Colombia near 07N745, moving westward at 20 kt. This wave has Saharan dust following the wave axis as observed in GOES-16 satellite imagery. No deep convection is presently noted with this wave over the Caribbean waters. Scattered moderate to strong convection is being enhanced over NW Colombia, including its nearby coastal waters from 07N-10N between 74W-78W. Isolated showers are possible elsewhere within 60-90 nm of its axis. A tropical wave pulling farther away from the region has its axis roughly along 91W S of 20N, moving westward at 10-15 kt. Only isolated showers and thunderstorms are noted within 90 nm east of this wave over northern and central Guatemala. Future details on this wave will be described in the eastern Pacific Tropical Weather Discussion. ...MONSOON TROUGH/ITCZ... The monsoon trough extends from W Africa near 18N16W to 10N21W to 07N30W, where latest scatterometer data indicates that the ITCZ begins and to 09N40W to 09N46W. It resumes west of the above described tropical wave at 08N49W to 06N55W. Scattered moderate isolated strong convection is within 240 nm southeast and south of the trough between 17W-20W. Scattered moderate convection is within 60 nm south of the ITCZ between 28W-34W, and also south of the ITCZ within 30 nm of line from 06N38W to 05N45W. ...DISCUSSION... GULF OF MEXICO... The western periphery of Atlantic high pressure ridging extends E to W over the central gulf waters.Light to moderate anticyclonic flow are over the gulf waters. Current NWS mosaic radar shows scattered moderate convection over the northern gulf north of 28N between 88W-91W. Isolated showers and thunderstorms are over the remainder of the gulf waters. Expect rather weak high pressure to prevail across the northern gulf waters through Thu. A surface trough will move westward off the Yucatan Peninsula each evening through Thu, enhancing nocturnal winds over the eastern section of the SW Gulf. CARIBBEAN SEA... Please read the Special Features section for details about pulsing gale force winds near the coast of Colombia. Aside from the tropical waves mentioned above, an upper level low is noted on water vapor imagery just to the south of the Yucatan Channel. Mainly fresh E winds will continue over the central Caribbean Sea and strong NE-E winds will be over the SW and S central sections of the Caribbean through Thu. ATLANTIC OCEAN... A weak surface trough over the W Atlantic extends from 32N59W to 29N65W. Scattered showers and isolated thunderstorms are within 60 nm of the trough. This trough will slowly weaken Tue as the supporting upper trough lifts to the NE away from it. High pressure will build in the wake of the trough. A large area of Saharan Air Layer (SAL) dust that is currently over the central Atlantic from 08N- 24N and between 45W- 60W will continue to translate westward through the rest of the week. A weaker area of dust from 09N-27N between the SE Bahamas and 60W is also moving westward. For additional information please visit http://www.hurricanes.gov/marine $$ Formosa/Aguirre