000 AXNT20 KNHC 110604 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0605 UTC Sat Sep 11 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 31N. The following information is based on satellite imagery, weather observations, radar and meteorological analysis. Based on 0000 UTC surface analysis and satellite imagery through 0600 UTC. ...SPECIAL FEATURES... Hurricane Larry is centered near 48.7N 53.2W at 11/0600 UTC or 70 nm NNW of St. Johns Newfoundland moving NNE at 41 kt. Estimated minimum central pressure is 963 mb. Maximum sustained wind speed is 70 kt with gusts to 85 kt. Most of the convection is over the northern semicircle. Numerous moderate with embedded isolated strong convection extends outward for 360 nm from the center, except to 120 nm in the SW quadrant. On the forecast track, the center of Larry will be moving quickly away from Newfoundland during the next several hours. Little change in strength is forecast today, and Larry is expected to become a strong extratropical low later this morning before it merges with another low over the Labrador Sea on Sunday. Swells generated by Larry will affect Bermuda, the east coast of the United States, and Atlantic Canada through tonight. These swells are likely to cause life-threatening surf and rip current conditions. Please read the latest High Seas Forecast issued by the National Hurricane Center at website https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml and the latest NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. A tropical wave extends along 91W from the W Yucatan Peninsula southward through Guatemala. This is southeast of a broad upper trough reaching from the lower Mississippi Valley to the western Bay of Campeche. The interaction of tropical wave with divergent flow aloft on the southeast side of the upper trough is supporting large clusters of showers and thunderstorms across the south- central Gulf of Mexico and northwest Caribbean Sea. Upper-level winds over the western Gulf of Mexico are expected to become more conducive for development over the weekend, and a tropical depression is likely to form on Sunday or Monday while the system moves northwestward and then northward near the coast of northeastern Mexico. Further development of this system will be possible through the middle of next week if it remains over water, and interests along the western and northwestern Gulf coast should monitor the progress of this system. The chance of tropical depression forming over the next 48 hours is high. Regardless of development, this disturbance is expected to produce heavy rain across portions of Central America and the Yucatan Peninsula today, which may lead to flash flooding and mudslides. By late this weekend, heavy rain will likely reach portions of the western Gulf coast. A strong tropical wave just off the coast of Africa, along 18W, is moving W at 10-15 kt. Scattered moderate convection is observed between Senegal and the Cabo Verde Islands. Environmental conditions appear generally conducive for additional development, and a tropical depression is likely to form late this weekend or early next week while the system moves generally westward over the far eastern Atlantic near the Cabo Verde Islands. Interests in the Cabo Verde Islands should monitor the progress of this system. The disturbance has a medium chance of development over the next 48 hours. ...TROPICAL WAVES... An Atlantic tropical wave has its axis along 39W, south of 22N and it is moving W at 15 kt. The wave is surrounded by dry and dusty Saharan air, inhibiting the development of showers and thunderstorms. Another Atlantic tropical wave has is axis along 57W, south of 21N and it is moving W at 15 kt. Recent scatterometer satellite data show a broad surface curvature, which is also evident on satellite imagery. A few showers are noted near the northern part of the wave between 55W and 61W. A Caribbean tropical wave has its axis along 76W, south of 16N and it is moving W at 10-15 kt. The interaction of this wave with the E Pacific monsoon trough is enhancing scattered moderate to isolated strong convection over N Colombia. ...MONSOON TROUGH/ITCZ... The monsoon trough passes through the coast of Mauritania near 19N16W to 09N28W and to 07N40W. No ITCZ segment is identified. Scattered moderate convection is noted south of the monsoon trough from 03N to 09N and between 21W to 31W. GULF OF MEXICO... A complex weather pattern is allowing for a large area of disorganized showers and thunderstorms across the S and SE Gulf of Mexico, especially from SW Florida to the Bay of Campeche. The strongest storms are actually inland over W Yucatan and SW Mexico. The surface features found in the Gulf are a stationary front that stretches across the N Gulf and a few showers are noted near this boundary. Also, a sharp trough extends from the Bay of Campeche near 18N94W to the NW Gulf near 27N94W. A recent scatterometer satellite pass show fresh to locally strong E-NE winds within 160 nm of the Yucatan peninsula, with the strongest winds found in the E Bay of Campeche, S of 21N. Gentle to moderate anticyclonic winds are found in the rest of the basin. Seas of 2-4 ft are noted in the Bay of Campeche, SE and NW Gulf waters, and 1-2 ft elsewhere in the Gulf. For the forecast, see the Special Features section above for information on the tropical wave that has potential to develop into a tropical cyclone over the southwest Gulf of Mexico Sunday or Monday. Elsewhere, a frontal boundary over the northern Gulf will prevail through Sun supporting showers and thunderstorms across the region. CARIBBEAN SEA... Please see the Special Features section above for details on the tropical wave over Yucatan and Guatemala that is inducing convection west of 85W. Weakening evening storms are seen near the Tiburon peninsula of Haiti and in the Windward Passage, and a few showers are seen off the NW coast of Colombia and NE Panama. The rest of the Caribbean Sea enjoys fairly tranquil weather conditions. A recent scatterometer satellite pass show a large area of strong to locally near gale- force trades in the south-central Caribbean, especially within 190 nm of the NW coast of Colombia and the Gulf of Venezuela. Seas in the area are 6-9 ft. Moderate to fresh trades are noted in the north-central and E Caribbean and the Bay of Honduras with seas of 4-6 ft. Gentle to moderate trades and seas of 2-4 ft are found elsewhere in the basin. For the forecast, the Atlantic ridge will continue to build westward across the Caribbean, bringing an increase in the trade wind flow this weekend. Fresh to strong winds will occur offshore Colombia and in the Gulf of Venezuela, mainly at night through Sun. Fresh to strong winds are also likely in the late evening in the Gulf of Honduras through Sun. Scattered showers and thunderstorms across the NW Caribbean are expected to reduce in coverage by Sat. ATLANTIC OCEAN... Please see the Special Features section above for details on Hurricane Larry over the NW Atlantic. A broad 1025 mb subtropical ridge is the dominant feature across the tropical Atlantic. A cold front extends from a 1011 mb low pressure near 35N68W to the Space Coast of Florida near Cape Canaveral. A few showers are noted along this boundary. A surface trough stretches from 16N49W to 1050W and scattered moderate convection is observed from 13N to 17N and between 47N and 51W. Satellite wind data show fresh to locally strong trades on the northern portion of the trough from 14N to 18N and between 45W and 53W. Moderate to fresh NE winds are noted E of 35W, from 19N to 27N. Gentle to moderate easterlies prevail in the rest of the basin. Seas of 4-7 ft is observed N of 14N and W of 35W, while seas of 5-8 ft is seen E of 35W. Seas of 3-6 ft are found elsewhere in the basin. For the forecast over the western Atlantic west of 65W, swells generated by Hurricane Larry will also subside by tonight. A frontal boundary will linger across the area through Sun which will bring showers and thunderstorms across the area through early next week. Otherwise, quiescent conditions will prevail through midweek. $$ DELGADO