241 AXNT20 KNHC 180458 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1257 AM EDT Wed Jul 18 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 0000| UTC surface analysis and satellite imagery through 0515 UTC. ...SPECIAL FEATURES... SW Caribbean Sea gale warning: A gale is in effect along the coast of Colombia from 11N to 13N between 70W and 76W, with seas 8 to 13 ft. The gale ends on 18/1200 UTC. The gale resumes on 19/0000 UTC, and ends again 19/1200 UTC. Please read the High Seas Forecast, under the AWIPS/WMO headers HSFAT2/FZNT02 KNHC, for more details. ...TROPICAL WAVES... A tropical wave is just off the coast of W Africa with axis extending from 20N18W to 07N20W. It is moving westward near 13 kt. A well defined 700 mb trough is noted in the model guidance over far western Africa. Latest satellite imagery is showing increasing cloudiness and convection in the vicinity of the wave. The observed cloud pattern is more typically characteristic of the presence of an ongoing W African monsoon trough, with the wave passing through it. The imagery shows scattered moderate convection within 120 nm east and 60 nm west of the wave from 08N- 10N. A major outbreak of Saharan Air Layer (SAL) dust envelops the wave environment north of 10N as seen in GOES-16 images. A central Atlantic tropical wave extends from 22N51W to 14N54W to 07N55W, 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 covering the area from 09N-23N between 43W-60W. The wave is being intruded upon by Saharan dust limiting significant convection from developing near it. Only scattered showers and isolated thunderstorms are seen within 180 nm to the east of the wave from 10N-12N, while isolated showers are within 30 nm of a line from 16N51W to 16N55W. A tropical wave axis over the central Caribbean extends from W Cuba at 22N82W to S of Panama at 06N81W, moving westward at 20 kt. Saharan dust is following in behind this wave axis as observed in GOES-16 satellite imagery. Scattered moderate to isolated strong convection is over Central America from from Honduras to Panama. ...MONSOON TROUGH/ITCZ... The monsoon trough axis extends from W Africa near 20N16W to 07N30W to 06N36W, where latest scatterometer data indicates that the ITCZ begins and continues to 08N45W to 10N53W. The ITCZ resumes west of a tropical wave at 10N56W and continues to South America near 09N60W. Scattered moderate convection is from 07N- 09N between 24W-30W. Similar convetion is from 03N-06N between 36W-48W. ...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 isolated strong convection over the northern gulf north of 28N between 86W-92W. Scattered moderate convection is over the far northeastern waters north of 28N and east of 84W. This convection is expected to remain for the next 24 hrs. Expect rather weak high pressure to prevail across the northern gulf waters through Thu. A surface trough will move westward off the Yucatan Peninsula Thu evening, enhancing nocturnal winds over the eastern section of the SW Gulf. CARIBBEAN SEA... Please read the Special Features section for details about the pulsing gale force wind events in the far SW Caribbean near the coast of Colombia. Aside from the tropical waves mentioned above, a small upper-level low is seen on water vapor imagery over the extreme northeastern part of the Yucatan Peninsula. Mostly 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. Low-cloud streamers with brief isolated showers will continue over the far eastern Caribbean through Thu. Scattered showers and thunderstorms will again develop over the interior sections of Hispaniola Thu afternoon. ATLANTIC OCEAN... A weak surface trough over the western Atlantic extends from near 32N57W to 29N60W. Scattered showers are within 60 nm of the trough axis. The trough will dissipate tonight as the supporting upper trough continues to lift northeastward. A 1032 mb high is well north of the area near 38N41W. Scattered showers and thunderstorms are north of 28N between 70W-80W due to an upper level trough that stretches along the U.S. eastern seaboard. This activity will remain active through Thu as a strong deep-layer trough moves off the eastern seaboard. High pressure will build in the wake of this trough. A large area of Saharan Air Layer (SAL) dust is currently over the central Atlantic from 09N-24N and between 48W-65W. The dust will continue to translate westward for the rest of the week. A more subtle batch of dust tracking westward is observed from 18N-27N between 60W and the Bahamas. For additional information please visit http://www.hurricanes.gov/marine $$ Formosa