Tropical Storm Sebastien is near 24.8N 57.0W at 22/0900 UTC, or about 520 nm northeast of the northern Leeward Islands, moving ENE at 13 kt. Minimum central pressure is 999 mb. Maximum sustained wind speeds are 50 kt with gusts to 60 kt. Numerous moderate with isolated strong convection is within 330 nm of the center in the northeast quadrant. Satellite imagery indicates the center is exposed with all convection to the northeast of the center. An ENE to northeast motion is expected during the next few days, along with gradual weakening. The public advisories for Sebastien are available via awips/wmo headers miatcpat5/wtnt35 kNHC. The forecast/advisories for Sebastien are available via the awips/wmo headers miatcmat5/wtnt25 kNHC.
An eastern Atlantic Ocean tropical wave is along 32/33W, moving west around 10 kt. The wave shows up well in tpw imagery and model diagnostics. Numerous moderate with scattered strong convection is seen from 00N-09N between 27W-36W. Isolated moderate convection is elsewhere from 00N-10N between 25W-39W.
Another, weaker tropical wave is along 42/43W from 05N-13N, moving w-nw around 10 kt. Isolated showers are near the wave axis.
An Atlantic Ocean tropical wave is along 54W from 13N southward, moving west at 10-15 kt. Isolated showers are within 120 nm of the wave axis.
A Caribbean Sea tropical wave is along 81W from 06N-16N, moving west around 10 kt. Isolated showers and tstorms are along and within 120 nm east of the wave axis from 12N-16N.
The Monsoon Trough passes through the coastal plains of Sierra Leone near 12W to 14W. The ITCZ continues from 14W to 31W, then continues west of a tropical wave from 35W to 46W. Aside from the convection mentioned above in the tropical waves section, isolated moderate convection is seen from 01N-09N between 07W-17W.
Gulf of Mexico
Deep-layered anticyclonic wind flow covers the basin. Scattered showers are over coastal areas of southeast Texas and portions of Louisiana, ahead of a cold front over central Texas. The latest ascat pass shows moderate to fresh southeast winds across the basin.
A surface ridge will prevail across the area through today, with fresh southeast return flow persisting over the western Gulf. A cold front will move off the Texas coast and into the northwest Gulf this evening, cross the northern and central waters this weekend, then weaken and stall over the southern Gulf sun night into mon. Another cold front may move into the northwest Gulf tue into tue night.
A cold front extends from 62W to Puerto Rico to 71W. The front continues as stationary to Jamaica. A surface trough extends southwestward from 56W to 62W to 70W. Isolated to scattered showers and tstorms are in between the front and the trough from 14N-18N between 60W-75W. The latest ascat pass shows strong n-ne winds in the mona and windward passages, and south of the Dominican Republic and Cuba.
The front in the northeast Caribbean will completely stall and weaken through tonight. Fresh northeast winds will prevail across the waters north of the front today, with the strongest winds expected through the windward and mona passages, as well as south of the Dominican Republic, as high pressure builds behind the front. Easterly trades will freshen across the south-central Caribbean early next week, increasing to strong tue into tue night.
Surface high pressure ridging covers the western Atlantic west of 65W, stemming from a 1022 mb high centered near 77W. Fresh north to northeast winds are throughout the Bahamas region. Strong north winds are from 20N-30N between 63W-70W. A cold front passes through 54W to 59W to 63W to Puerto Rico. The front is just a short distance west of t.s. Sebastien. Aside from the convection mentioned in the section above associated with Sebastien, scattered moderate convection is along and within 180 nm east of the cold front north of Sebastien to 32N. A surface trough that trails from the southern side of t.s. Sebastien extends from 56W to 62W to 70W. Scattered showers and tstorms are near the trough axis.
Farther east, an upper-level low near 41W is inducing scattered showers and isolated tstorms from about 13N-25N between 30W-43W. North of that, fair weather prevails due to a 1021 mb high centered near 33W. A cold front extends from 11W to the canary islands near 15W to 21W to 26W with no significant precipitation noted.
Sebastien will continue to accelerate northeastward away from the forecast waters today. The cold front from 59W to 63W to Puerto Rico will continue moving eastward and steer Sebastien into the central Atlantic. High pressure will build behind the cold front across the northern waters through sat, then shift eastward sat night. The next cold front will cross the western Atlantic sun through mon, weakening near 70W tue and tue night.
Posted 14 hours ago by NHC Forecaster Hagen