000 AXNT20 KNHC 282344 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 744 PM EDT Wed Jun 28 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 1800 UTC surface analysis and satellite imagery through 2315 UTC. ...SPECIAL FEATURES... Please refer to the METEO-FRANCE High Seas Forecast, that is listed on the website: WWW.METEOFRANCE.COM/PREVISIONS-METEO- MARINE/BULLETIN/GRANDLARGE/METAREA2. Gale Warning: N winds increasing to gale force tonight in AGADIR AND TARFAYA through 30/0000 UTC. The OUTLOOK, for the 24 hours that follow the forecast that is valid until 01/0000 UTC, consists of: the threat of severe N gale over AGADIR and TARFAYA. N or NE gale increasing over eastern MADERIA and CANARIAS. ...TROPICAL WAVES... A tropical wave over the far eastern Atlantic near the coast of Africa has become somewhat tilted in a northwest to southeast fashion during the day since its northern vorticity lobe moved off the coast of Africa on Tuesday evening, with its axis extending from 20N17.5W to near 09N16W. It is moving westward at 10-15 kt. The wave is embedded within a rather large envelope of deep moisture as seen in the latest satellite animation. Moist southwesterly flow is noted across the southern extension of the wave axis where it crosses the monsoon trough. Large clusters of scattered moderate to strong convection are seen along and east of the wave axis to inland the coast of Africa from 10N to 15N. Scattered moderate isolated strong convection is within 60 nm east of the axis from 09N to 10N. A tropical wave over the central Atlantic has its axis extending from 14N38W to near 02N39W, moving westward near 13 kt. Satellite imagery and TPW data indicate that moisture around the wave is not as deep as 24 hours ago due to a large area of Saharan dust that intruded from the north towards the wave. The last visible imagery showed elongated cyclonic turning of the low clouds around the vicinity of the wave. Only isolated showers and thunderstorms are noted within 120 nm east of the wave from 10N to 14N, and within 120 nm either side of the wave south of 14N. A broad and rather robust tropical wave has its axis tilted in a northeast to southwest position as it moves across the Lesser Antilles. The axis extends from just east of Martinique through the Windward Islands, to just west of Trinidad and Tobago and to inland the northeast part of Venezuela. The wave moved an average speed of about 16 kt during the past 24 hours, and is maintaining a similar speed as of this evening. This wave continues to be easily identifiable on satellite imagery as having the typical configuration of those waves observed later during the season. It is detected in the model fields, and is again further supported by the latest diagnostic model analysis. This wave is accompanied by scattered to moderate to isolated convection within 120 nm to its east from 12N to 16N, and within 60 nm to its west from 12N to 14N. Some of this activity may most likely be attendant by strong gusty winds. The wave is forecast to move across the eastern Caribbean tonight through much of Friday, and the eastern half of the central Caribbean Friday night. Expect increasing showers and thunderstorms, with gusty winds, to move across these waters. A tropical wave over the western Caribbean Sea has its axis along 85W south of 21N, moving westward at about 10 kt. The axis of this wave continues to mark the leading edge of a surge of deep tropical moisture. Scattered moderate to isolated strong convection is evident to the east of axis from 11N to 15N west of 80W to inland the eastern and central sections of Honduras and Nicaragua. Scattered showers and isolated thunderstorms are seen within 60 nm east of the axis from 15N to 17N. Some of the convective activity over Honduras and Nicaragua may contain locally heavy rainfall. The shower and thunderstorm activity approaching those same countries from offshore may bring gusty winds and locally heavy rainfall tonight through at least Thursday afternoon. The tropical wave axis earlier analyzed along 95W/96W has moved further into the eastern Pacific, and is being discussed under the eastern Pacific Tropical Weather Discussion. ...ITCZ/MONSOON TROUGH... The Monsoon Trough axis extends from the coast of Africa near 14N17W to 10N23W. The Intertropical Convergence Zone then extends from 10N22W to 10N32W to just east of the tropical wave along 38W/39W, and continues from just west of the same wave to 05N45W to 05N51W. Other than convection associated with the tropical waves discussed above, scattered moderate isolated strong convection is within 120 nm north of the axis between 47W- 51W. Scattered moderate convection is within 180 nm south of the Monsoon Trough axis between 18W-32W. ...DISCUSSION... ...THE GULF OF MEXICO... A mid to upper level trough is evident on water vapor imagery to be just inland the Texas and southwest Louisiana coasts. A jet stream branch with strong southwest to west winds is seen just east of this trough, and stretches northeastward over the western Gulf, and eastward over the north-central and northeastern Gulf. A dissipating stationary boundary has drifted northward to inland Louisiana and to just along the Florida panhandle coastline. A surface trough over the far western Gulf waters is supported by the aforementioned mid to upper level trough. Visible satellite imagery from this afternoon along with observations from buoys indicated that weak surface low of 1011 mb formed along the far western Gulf surface trough that extends from just southwest of Galveston to just northeast of Brownsville. The surface analysis reveals a weak pressure pattern present elsewhere across the Gulf. A large area of scattered moderate to isolated strong convection is confined to the much of the NW Gulf north of about 25N and west of 90W. This activity increased quite impressively during today, and is gradually spreading towards the north-central Gulf waters. This activity is capable of producing strong gusty winds. Isolated showers and thunderstorms are seen east of 90W, and also south of 25N west of 90W. With little changes to the present synoptic pattern forecast through Friday, the convection described over the NW Gulf is expected to continue through most of Friday as it shifts to more to the north central Gulf. ...THE CARIBBEAN SEA... The main feature presently in the basin is a strong tropical wave just entering the southeastern Caribbean and another tropical wave over the western Caribbean near 85W south of 21N. These features are discussed in the section above. Aside from the convection related to the tropical waves and isolated showers and thunderstorms occurring elsewhere over the NW Caribbean, generally fair weather prevails elsewhere. Scatterometer data depicts moderate to fresh trades across the basin, except in the SW Caribbean from 11N to 15N between 72W and 80W where a stronger gradient present there is supporting strong northeast to east winds. Little change is expected with these winds through Friday. The tropical wave entering the southeastern Caribbean will be the main feature during the next 48 hours. Scattered showers and isolated thunderstorms are noted well ahead of the wave affecting the waters south of 15N and east of 70W. This activity will continue to spread westward through Thursday. The impacts of this wave as related to marine interests will be mainly highlighted in the offshore and high seas forecasts in the the Marine Weather Discussion. ...HISPANIOLA... Isolated thunderstorms are observed over the interior of the island as some dry air has filtered in from the north. Guidance suggests that little change is expected in the present weather pattern through the next 24 hours, then increasing moisture along with scattered showers and thunderstorms are expected on Friday as a strong tropical wave approaches the island. ...THE ATLANTIC OCEAN... A large eastern Atlantic upper-level cyclonic circulation is located about 900 nm to the west of the western edge of the Canary Islands. A trough extends from the cyclonic center to near 10N41W. Isolated showers are possible within 300 nm of the circulation. Another upper-level cyclonic circulation is near 31N57W, and is transitioning to a trough with time. An upper level trough extends from the cyclonic center to 24N57W to 22N62W to 21N75W. A surface trough is analyzed from 29N59W to 22N61W. Scattered showers and isolated thunderstorms are noted east of the surface trough and south of the upper cyclonic circulation from 24N to 29N between 52W and 57W. A stationary front extends from near 32N74W to inland Florida between Saint Augustine and Daytona Beach. The front is supported by broad upper troughing just north of the area west of 68W. A surface trough is southeast of the frontal boundary from near 32N71W to the NW Bahamas. Plenty of moisture and instability is present over the this portion of the area, with all the ingredients being conducive to the development of scattered showers and thunderstorms to be present northwest of a line from 32N64W to 27N73W to South Florida. This activity is expected to continue through late Thursday before central Atlantic high pressure builds back to the west along 28N on Friday. Otherwise, the wind flow pattern around the southern periphery of high pressure that dominates the central and eastern portions of the basin will continue to transport Saharan African dust westward to the the central Atlantic by Friday. For additional information please visit http://www.hurricanes.gov/marine $$ Aguirre