000 AXNT20 KNHC 162357 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 0005 UTC Fri Sep 17 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 1800 UTC surface analysis and satellite imagery through 2350 UTC. ...SPECIAL FEATURES... Post-Tropical Cyclone Nicholas is centered near 29.9N 92.5W at 2100 UTC or 80 nm S of Alexandria Louisiana moving NNE at 4 kt. Estimated minimum central pressure is 1009 mb. Maximum sustained wind speed is 20 kt with gusts to 25 kt. A surface trough extends SW from the low pressure to the coastal waters of NE Mexico. Scattered showers and tstms are ahead of the surface trough covering the remainder basin. Moderate S to SW winds are over the north-central gulf with locally fresh winds over Mississippi and Alabama adjacent waters where the strongest convection is observed. The convection associated with the remnants of Nicholas will continue to affect the gulf through Sat. This convective activity is expected to produce additional rainfall amounts of 2 to 4 inches across the central Gulf during this period with isolated amounts to 6 inches possible. The Weather Prediction Center is issuing bulletins on Nicholas and they can be found at http://www.wpc.ncep.noaa.gov. Shower and thunderstorm activity associated with a broad area of low pressure located a couple of hundred miles SSE of the Outer Banks of North Carolina have changed little in organization this evening and the system still lacks a well-defined center. However, environmental conditions are becoming more conducive for development, and a tropical depression is likely to form during the next day or so while the system moves NNE off the SE and mid- Atlantic U.S. coasts. Regardless of development, this system could bring high surf to portions of the southeast and mid- Atlantic U.S. coasts through this weekend. Additional information on this system, including gale warnings, can be found in High Seas Forecasts issued by the NOAA Ocean Prediction Center. Please read the latest Tropical Weather Outlook at www.hurricanes.gov for more details. A tropical wave is in the Atlantic Ocean along 37W from 02N to 17N, moving west at 15 to 20 kt. Showers and thunderstorms remain disorganized and somewhat limited in association with this tropical wave and area of low pressure W of it. However, environmental conditions are expected to be conducive for development during the next few days, and a tropical depression could still form over the weekend. This system is expected to move westward to west-northwestward across the tropical Atlantic during the next several days and have a medium chance of tropical cyclone formation in the next 48 hours. Please read the latest Tropical Weather Outlook at www.hurricanes.gov for more details. ...TROPICAL WAVES... A tropical wave associated with a 1010 mb low SE of the Cape Verde Islandsis generating disorganized cloudiness and thunderstorms over the far eastern tropical Atlantic. Latest scatterometer data show fresh to locally strong NE winds to the N of the low pressure as the gradient tightens with the ridge to the north. Environmental conditions are forecast to be only marginally conducive, and development, if any, of this system should be slow to occur over the next few days while the system moves WNW over the far eastern Atlantic. A tropical wave is in the W Caribbean Sea along 79W from 19N southward to Panama, moving west at 10 to 15 kt. Scattered showers and thunderstorms are NE of the wave axis over E Cuba and Hispaniola. Isolated showers are over the SW Caribbean. ...MONSOON TROUGH/ITCZ... The monsoon trough extends from 14N17W to 11N33W to 06N44W. The ITCZ continues from 06N46W to the coasts of French Guiana and Suriname. For information about convection, refer to the tropical waves section. GULF OF MEXICO... The Weather Prediction Center is issuing bulletins on Post Tropical Nicholas, located over SE Louisiana. Refer to the Special Features section above for details. Aside from the shower activity associated with the remnants of Nicholas and the enhanced winds over the north-central Gulf, light to gentle variable winds dominate the remainder basin except for the Yucatan Channel and adjacent waters where moderate to locally fresh SE are observed. These winds will shift W to the SW basin through Sat and then diminish to light to gentle. Weak surface high pressure will establish across the basin Sun and prevail through early next week along with gentle to moderate winds. CARIBBEAN SEA... Refer to the Tropical Waves section above for details on a tropical wave moving across the Caribbean Sea. Morning scatterometer winds showed fresh easterly winds across the central Caribbean between the tropical wave along 79W and 70W, and fresh SE winds across the outer Gulf of Honduras to just offshore of Cozumel, Mexico. Gentle trade winds prevail elsewhere. Seas are generally 2-4 ft, except 5-6 ft in the areas of strongest trade winds are blowing. Showers and thunderstorms continue to flare-up over the NW Caribbean due to a combination of a tropical wave moving westward across the basin and an upper-level low trough currently extending SW across the western basin. A tropical wave across the central Caribbean will move across the western Caribbean into the weekend. Another tropical wave will move across the Lesser Antilles this weekend. Strong winds will pulse in the overnights into early next week offshore Colombia and in the Gulf of Honduras. Low pressure in the eastern Atlantic is likely to develop into a tropical depression over the next couple of days, and this could bring increasing winds and seas to the waters near the Leeward Islands for the start of next week. ATLANTIC OCEAN... Refer to the Special Features section above for details on the disturbance situated northeast of the Bahamas, and the system in the eastern Atlantic. Both systems have a high chance of tropical cyclone formation through 48 hours. A ridge along about 36N dominates the Atlantic forecast waters E of 65W, with the main high pressure center of 1031 mb just south of the Azores. A surface trough continues to move westward across the tropical Atlantic and extends from 26N37W to 17N39W. A cluster of scattered showers and a few thunderstorms is noted over northern portions of the trough. Scatterometer data depicted very well the wind shift associated with the trough axis. Moderate to fresh NE-E winds are noted east of the trough to offshore of Africa. Seas are in the 6 to 8 ft range across this area. West of 65W, morning scatterometer winds depicted gentle moderate winds between the Bahamas and 65W, except fresh southerly winds north of 28N between the trough and 65W. Seas are generally 3 to 5 ft except 5 to 7 ft north of 27N in the fresh southerly wind flow. Showers and thunderstorms are increasing in association with low pressure several hundred miles SSE of the Outer Banks of North Carolina. A tropical depression is likely to form, however this system is moving northward out of the basin, so any increased winds and seas will be north of the area by Fri. Elsewhere, weak high pressure will lead to gentle to moderate mainly easterly winds across the basin. Another low pressure may impact waters north and east of the Leeward Islands early next week. $$ Ramos