000 AXNT20 KNHC 111802 TWDAT 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... A tropical wave extends from 21N92W to Mexico near 18N93W and into the Pacific Ocean near 16N94W. An upper-level trough extends from the coast of Texas to central Mexico. Upper-level diffluence east of the upper-trough in combination with the tropical wave are producing disorganized scattered moderate and isolated strong showers and thunderstorms over portions of the southern and central Gulf of Mexico, and southeastern Mexico. A recent ASCAT pass shows fresh E to SE winds between the wave axis and the west coast of the Yucatan Peninsula. Upper-level winds are expected to become more favorable during the next day or so, and a tropical depression is likely to form Sunday or Monday while the disturbance moves northwestward and then northward near the coast of northeastern Mexico. Further development is 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. Expect an increase in winds and seas along these regions with this system. Regardless of development, the disturbance is expected to produce heavy rain across portions of the Yucatan Peninsula through today, which may lead to flash flooding. By late this weekend, heavy rain will likely reach portions of the western Gulf coast, including coastal Texas and Louisiana through the middle of next week. Localized significant rainfall amounts are possible, potentially resulting in areas of flash and urban flooding. The chance of tropical cyclone formation within the next 48 hours is high. A tropical wave with an axis along 21W from 21N southward is moving W at 15-20 kt and is producing a concentrated but disorganized area of showers and thunderstorms from 12N-17N between 18W-23W, which is now just reaching the eastern Cabo Verde Islands. Environmental conditions appear generally conducive for gradual development, and a tropical depression is likely to form late this weekend or early next week while the system moves westward over the far eastern Atlantic. Regardless of development, gusty winds and locally heavy rain are expected across the Cabo Verde Islands through tonight. The chance of tropical cyclone formation within the next 48 hours is medium. Larry has transitioned to an extratropical cyclone as of 1500 UTC today, and the final NHC advisory has been issued. The position is near 54.0N 48.2W at 1500 UTC, or about 480 nm NNE of Cape Race, Newfoundland, moving NNE at 42 kt. Estimated minimum central pressure is 963 mb. Maximum sustained wind speed is 60 kt with gusts to 75 kt. Larry is expected to merge with another extratropical low tonight or early Sunday. Significant swells from Larry will continue affecting portions of 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 see the final NHC advisory at www.hurricanes.gov for more details. ...TROPICAL WAVES... See the section above for details on the two tropical waves with potential for development, currently located along 21W and 92W. An Atlantic tropical wave has an axis along 42/43W from 05N-23N, moving W at 15 kt. The wave is surrounded by dry Saharan air, which is inhibiting convection at this time. An Atlantic tropical wave has an axis along 61W from 05N-21N, moving W at 20 kt. This wave is moving westward in sync with an upper-level trough. Satellite imagery and ASCAT data show broad surface curvature with this wave. Scattered moderate convection is noted from 16N-22N between 56W-66W. A Caribbean tropical wave has an axis along 78W from 15N southward, 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 the SW Caribbean, south of 12N. ...MONSOON TROUGH/ITCZ... The monsoon trough passes through the coast of Mauritania near 19N16W to 13N26W to 06N34W. The ITCZ continues from 06N34W to 06N41W. Aside from the convection noted in the sections above, scattered moderate convection is seen from 05N-08N between 26W-38W. GULF OF MEXICO... See the Special Features section above for details on the tropical wave over the eastern Bay of Campeche and a description of the upper-level trough in the area. In addition to those features, a surface trough extends from NE Mexico near 26N98W to 20N95W. A stationary front extends from Cedar Key Florida near 29N83W to 28N94W. Expect the frontal boundary to prevail through Sunday. Scattered moderate and isolated strong convection cover much of the Gulf of Mexico south of 27N. An area of numerous moderate to scattered strong convection is in the Bay of Campeche from 18N-21N between 92W-95W, associated with the tropical wave. Other than the fresh winds in the Bay of Campeche, mainly moderate wind speeds prevail elsewhere. Recent buoy observations and altimeter data show seas of 3 to 4 ft across much of the basin, but seas up to 5 ft could be occurring in the eastern Bay of Campeche. CARIBBEAN SEA... Please see the Tropical Waves section above for details on the tropical waves along 61W and 78W. Scattered moderate convection is occurring over the NW Caribbean north of 20N west of 84W due to the tropical wave over the eastern Bay of Campeche. That convective activity will diminish later today. Scattered tstorms are occurring near the Virgin Islands, Puerto Rico and the Dominican Republic due to an upper-level low/trough moving westward across the area. Subsidence and drier air is found over most of the central Caribbean. A recent ASCAT pass shows strong trades in the south-central Caribbean from 11N-15N between 71W-78W, where seas are 6 to 9 ft. Buoy 42058 near 14.4N 74.8W is reporting E wind 21 kt and seas of 8 ft at 1700 UTC. Fresh to strong east to southeast winds are seen in the Gulf of Honduras, where seas are 5 to 6 ft. Moderate trades prevail across the remainder of the basin, with 3 to 5 ft seas. 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. ATLANTIC OCEAN... West of 60W: A cold front extends from 31N67W to 30N69W, with a stationary front from 30N69W to Cape Canaveral Florida. Isolated showers and thunderstorms are near and north of the front. Expect the showers and storms to linger through Mon while the front remains over the area. Moderate NE to E winds are north of the front. Gentle E to SE winds are south of the front. An upper-level low spinning near 21N64W is moving westward along an upper-level trough. Isolated thunderstorms cover the area south of 25N between 62W-79W. Gentle winds prevail from 24N-29N, due to weak surface ridging. ASCAT shows moderate trade winds south of 24N and west of 65W. Seas of 4 to 6 ft prevail over northern portions of the area as the swell from Larry subsides. Seas are 3-5 ft south of 25N west of 65W. East of 60W: A surface trough is analyzed from 11N53W to 17N51W. Scattered moderate convection is seen from 13N-18N between 49W-56W. A surface high pressure ridge extends across the subtropics from 29N22W to 28N60W with gentle wind speeds north of 27N. Fresh trades are from 20N-25N between 20W-45W, and from 14N-22N between 49W-61W. Seas are 5 to 8 ft in the area of fresh winds. Forecast west of 60W: An area of low pressure is expected to form near the southeastern Bahamas in a few days. Gradual development of this system is possible thereafter as it moves northwestward across the western Atlantic. See the latest NHC Tropical Weather Outlook at www.hurricanes.gov for details. $$ Hagen