741 AXNT20 KNHC 061718 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 1805 UTC Mon Sep 6 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 1200 UTC surface analysis and satellite imagery through 1700 UTC. ...SPECIAL FEATURES... Hurricane Larry is centered near 22.1N 52.9W at 1500 UTC, moving NW at 9 kt. Estimated minimum central pressure remains 956 mb. Maximum sustained wind speed is 105 kt with gusts to 130 kt. The large eye diameter is 60 nm on IR satellite imagery. Numerous moderate to strong convection is noted within 150 nm SW and 120 nm NE semicircles. Seas of 12 ft or higher extend outward 300 to 330 nm from the center in the N semicircle, and 270 nm across the S semicircle, with maximum seas estimated at 46 ft. On the forecast track, a northwest motion with a slight decrease in forward speed is expected during the next few days, passing east of Bermuda. Minor fluctuations in strength are forecast during the next day or so, followed by very gradual weakening. Swells generated by Larry are reaching the Lesser Antilles and are expected to spread westward to portions of the Greater Antilles, the Bahamas, and Bermuda later today and Tuesday. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek. These swells are expected to cause large and dangerous surf which will produce life-threatening rip currents. 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. ...TROPICAL WAVES... An eastern Atlantic Ocean tropical wave has an axis along 26W-27W, from 19N southward, moving W around 15 kt. A 1013 mb low along the wave was depicted near 11N27W by a recent ASCAT pass, and also showed evidence of the wave at the surface. Scattered moderate isolated strong convection is noted along the trough from 05N to 10N between 21W and 33W. Scattered moderate convection is noted NW of the low from 12N to 15.5N between 26.5W and 29W. A central Atlantic Ocean tropical wave has an axis along 45W, from 17N southward, moving W at 10 to 15 kt. The wave is situated at the leading edge of a Saharan dust plume, so no significant convection is associated with this wave. Recent ASCAT data showed NE winds of 15 to 20 kt at the surface immediately behind the wave. A Caribbean Sea tropical wave has an axis along 82W, south of 18N through western Panama, moving W at 10 kt. Scattered moderate to strong convection extends from the eastern Pacific Ocean near 06N to 16N in the Caribbean between 74W and 83.5W. Recent ASCAT data shows an easterly wind surge of 15 to 20 kt behind this wave, which is aiding in forcing convection there. ...MONSOON TROUGH/ITCZ... The monsoon trough extends into the Atlantic Ocean off the coast of Africa, along the border of Mauritania and Senegal near 16.5N 16.5W, to low pressure along a tropical wave near 11N27W to 06.5N34.5W. The ITCZ extends from 06.5N35W to 04N47W to 04.5N54W. Aside from the convection mentioned in the Tropical Waves section above, scattered moderate isolated strong convection is noted from 04N to 07N between 35W and 44W and from 05N to 09.5N between 48W and 54W. GULF OF MEXICO... A weak 1017 mb high is centered across the extreme SE Gulf and adjacent SW Florida coast. A surface trough extends across the eastern Bay of Campeche to near 23N92W, while a stalling frontal boundary is along the SW Louisiana coast extending NE across south Mississippi. The modest pressure gradient between these features is producing gentle to moderate S to SW winds across the S central and east portions of the Gulf, around the periphery of the high. A middle to upper level cyclone is cut off across the central Gulf along about 90W and is promoting scattered showers and thunderstorms across central portions from 22N to 27N between 84W and 90W, and to the east of the surface trough, between it and the W coast of the Yucatan Peninsula. The surface trough off the NW coast of the Yucatan Peninsula is forecast to move N or NE over the central and NE Gulf of Mexico over next few days, likely reaching the northern Gulf coast by mid-week. Upper-level winds are currently unfavorable for tropical development, but could become somewhat conducive for formation before it reaches the coast. Aside from this low pressure, high pressure will bring light to gentle winds and slight seas into mid-week. CARIBBEAN SEA... See the Tropical Waves section above for details on the tropical wave moving into the western Caribbean. A very modest pressure gradient across the basin between high pressure south of Bermuda and low pressure along the monsoon trough exiting NW Colombia is yielding moderate to fresh trade winds across the basin between 65W and 80W, where seas are generally 4 to 7 ft. Swell from distance hurricane Larry is beginning to enter Atlantic passages off the Leeward Islands, where seas of 5 to 7 ft are occurring. Buoy 42060 located WSW of Montserrat is currently reporting E swell of 3 ft at 13 seconds. An upper level trough extends from the Atlantic north of Puerto Rico southwestward across Hispaniola to offshore of Honduras and Nicaragua. This upper level pattern is supporting the convection described with and behind the tropical wave along 82W. Moderate NE winds are converging across the Leeward Islands and the adjacent NE Caribbean where small clusters of moderate thunderstorms are occurring. Major Hurricane Larry will remain well to the northeast of the Leeward Islands today and tonight and continue moving northwestward and farther north of the area through mid week. Associated moderate to large swell will continue to spread west and southwestward across the Leeward Islands and Atlantic passages into mid week. Elsewhere, gentle to moderate trade winds will persist, pulsing to fresh winds off Colombia mainly at night. ATLANTIC OCEAN... Please see the Special Features section for details on Category 3 Hurricane Larry. A middle to upper level cyclone is located west of Larry, is centered near 22.5N 66W and nearly stationary. A small middle to upper level cyclone can be seen in satellite imagery moving slowly NE and off the central coast of Florida. Associated upper level divergence associated with both of these features is supporting active scattered convection from 25N to 30N between 65W and 72W, where moderate SW to W winds are converging at the surface south of a weak trough. Small scattered clusters of moderate convection are also across the NW Bahamas and extend N to offshore of Florida to 29N. At the surface, weak high pressure is drapped across the north of Larry, with weak high centers of 1018 mb near 25N64W and another 1018 mb high near 25N41W. Thus, generally outside of Larry, light to gentle wind prevails with seas of 3 to 7 ft west of 66W. Buoy 43043 located NNE of San Juan, Puerto Rico is reporting eastern swell approaching 8 ft at 15 seconds. Smaller east swell of this wave length will reach the SE Bahamas and adjacent waters to the north this afternoon. To the S and E of Larry, generally S of 20N and E of 50W, moderate to fresh NE trades prevail. A weakening cold front is noted in the northeast basin, from 30N18W to 27N27W to 30N37W. No convection is associated with this front, and winds north of the boundary are N and gentle to moderate. Major Hurricane Larry will move to 23.1N 54.0W this evening, 24.5N 55.3W Tue morning, 25.9N 56.6W Tue evening, 27.5N 58.0W Wed morning, 29.3N 59.6W Wed evening. Larry will move north of the area near 31.6N 61.2W Thu morning. Large swell generated by Larry will continue to propagate westward across waters north through northeast of the Leeward Islands and spread west of 68W this afternoon, reaching 72W by mid week. $$ Stripling