AXNT20 KNHC 121126

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1205 UTC Mon Apr 12 2021

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 1115 UTC.


Windward Islands Ashfall Advisory: La Soufriere volcano on the island of Saint Vincent near 13.3N 61.2W is currently undergoing frequent eruptions. Volcanic ash may be reaching the ocean surface and low level visibility may be reduced. Mariners traveling within the area 18N39W to 08N40W to 10N50W to 15N62W to 17N45W to 18N39W are urged to exercise caution, especially west of 50W where the densest ash is being observed. If mariners encounter volcanic ash or floating volcanic debris, you are urged to report the observation to the National Hurricane Center by calling 305-229-4424.


The monsoon trough axis extends southward from the coast of Senegal near 13N17W to 05N21W, where overnight scatterometer data indicates that it transitions to the ITCZ to 00N30W and to 00N45W. Scattered moderate to isolated strong convection is noted from 05S-03N between 18W-26W and from 03S to 00N between 26W-30W.


A weak cold front extends from northern Florida south-southwest to near 25N92W, where it transitions to a dissipating stationary front to inland Mexico at 25N98W. An overnight ASCAT pass indicated gentle wind speeds on both sides of the front. The front will reach from the southeastern Gulf to the central Gulf this afternoon and evening and to just SE of the Gulf tonight. As of 1100 UTC, an E to W oriented squall line extends from extreme southwest Florida to 26N85W. The squall line, in combination with forcing aloft from a shortwave trough, is generating a large convective complex that consists of numerous moderate to isolated strong type convection from 23N-26N between 81W-85W as 11Z. The convective complex is moving slowly southeastward. It has a history of producing frequent lightning and strong wind gusts. Scattered moderate showers extend eastward from the squall line over South Florida. Elsewhere, a weak surface trough is located in the SW Gulf of Mexico with its axis analyzed from 24N90W to inland Mexico at 19N97W. Wave heights are in the range of 3-5 ft across the Gulf of Mexico, except for lower wave heights of 1-3 ft in the southern Bay of Campeche.


See the Special Features section above for details on an Ashfall Advisory issued for ongoing volcanic eruptions on St. Vincent.

The latest surface analysis depicts a rather weak pressure gradient across the basin. Overnight ASCAT data highlighted moderate to fresh trade winds over the central Caribbean and fresh to strong southeast winds in the Gulf of Honduras. It revealed moderate trade winds elsewhere across the basin. Mainly fair weather conditions are in place across the basin, except for isolated shower and thunderstorm activity that is occurring over the far southwestern Caribbean along the coast of Panama. Wave heights are in the 4-6 ft range across most of the basin, except up to 7 ft in some locations in the south-central Caribbean.

For the forecast, fresh southeast winds will continue over the northwestern Caribbean through the period, while fresh to strong east to southeast winds continue in the Gulf of Honduras. Winds will pulse to strong speeds over a small area near the coast of Colombia during the afternoons and at night through Thu. Elsewhere, generally moderate to fresh east winds will change little through Fri night.


See the Special Features section above for details on an Ashfall Advisory issued for ongoing volcanic eruptions on St. Vincent.

Upper-level diffluence to the east of Florida is sustaining weaker convection than what was noted earlier over the central Bahamas. The latest satellite imagery shows scattered moderate convection moving offshore South Florida to the NW Bahamas, and extending from there southwestward to just east of South Florida and to over sections of the middle and upper Florida keys. Scattered showers and isolated thunderstorms are seen elsewhere west of 70W from 23N-32N. Expected for additional convective activity to move offshore South Florida this morning. An overnight ASCAT data pass detects a large area of fresh to locally strong south to southwest winds to the east of northern and central Florida, mainly north of 26N extending eastward to about 72W. A 1015 mb high pressure center is analyzed near 25N57W. A ridge extends from the high westward to the southeastern Bahamas. The ASCAT data pass also depicts moderate anticyclonic winds to the east of the southeastern Bahamas. Wave heights are 6-8 ft north of the Bahamas between 70W-77W.

For the forecast west of 65W, fresh to strong southwest winds east of northern and central Florida will shift eastward today ahead of a cold front that will move off the southeastern U.S. coast this morning. The front will reach from near 31N73W to the northern Bahamas and to South Florida early this afternoon, from near 31N67W to the southeastern Bahamas and to eastern Cuba by late tonight and the southeast part of the area on Tue. The front will move east of the forecast waters on Wed as weak high pressure builds in behind it, and as another cold front approaches the far northwest waters. This front will move across the water N and NE of the Bahamas from late Wed night through Fri night. Fresh to strong southwest winds are expected ahead of this front.

Farther east, a surface trough is analyzed from 26N45W to 22N56W. Isolated showers are possible near the trough between 50W-56W. Another surface trough is analyzed from 27N30W to 22N38W and to near 18N49W. A rather potent upper sub-tropical jet stream branch passes to its southeast as it stretches northeastward around the western periphery of a broad upper anticyclonic located over the far eastern Atlantic. The jet stream branch is advecting ample mid and upper-level moisture northeastward across and to the east of the trough. There is enough jet dynamics and lift for scattered showers and possible isolated thunderstorms to exist underneath the mid and upper-level moisture, namely from 20N to 28N between 27W-32W, also from 27N to 31N between 22W-27W and from 20N-25N between 32W-36W. An ASCAT pass from last night shows a swath of southwest to west 20-25 kt winds over the area north of 30N between 36W-40W. These winds are on the outer periphery of a tight gradient that surrounds a deep low pressure system located north of the discussion area. Wave heights are in the range of 10-12 ft with these winds. Northerly swell over the central Atlantic will diminish today as the low moves toward the northeast and weakens. A 1019 mb high pressure center is over the Canary Islands. A ridge extends from this high center to 24N25W and to 21N34W. The overnight ASCAT pass highlights light to gentle winds in anticyclonic fashion across the ridge axis.

$$ Aguirre