AXNT20 KNHC 170552

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0605 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 0000 UTC surface analysis and satellite imagery through 0530 UTC.


Post-Tropical Cyclone Nicholas is centered near 30.7N 92.4W at 0300 UTC or 35 nm S of Alexandria Louisiana and moving N at 4 kt. Estimated minimum central pressure is 1009 mb. Maximum sustained wind speed is 15 kt with gusts to 25 kt. A surface trough extends east-southeastward from Nicholas to the coastal waters just S of SE Alabama-Florida Panhandle. Scattered showers and isolated thunderstorms are seen across S Louisiana, central Mississippi and Alabama, Florida Panhandle and the N central Gulf. Moderate to locally fresh S winds and seas up to 4 ft are expected in the Gulf near these thunderstorms. The convection associated with the remnants of Nicholas will continue to affect these Gulf States through Sun with up to 3 inches of rain possible. The Weather Prediction Center is issuing bulletins on Nicholas and they can be found at http://www.wpc.ncep.noaa.gov/tropical/tropical_advisories.php?storm=NICHOLAS

A broad area of low pressure is located about 100 miles southeast of the Outer Banks of North Carolina. Although the circulation of this system has become a little better defined since yesterday, the associated showers and thunderstorms remain disorganized and located mainly well to the east of the center. 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 northward to north-northeastward off the southeast 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.

Showers and thunderstorms remain disorganized in association with a tropical wave and broad area of low pressure located about 1100 miles west-southwest of the Cabo Verde Islands. 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 at 15 to 20 mph across the tropical Atlantic during the next several days and has 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.


A tropical wave is near 15W from N Mauritania southward across Senegal coast into the Atlantic Ocean, and moving W at 5 to 10 kt. Scattered moderate convection is found from 07N to 14N between S Senegal/Guinea-Bissau and 19W.

An Atlantic tropical wave is along 40W from 17N southward and moving W near 15 to 20 kt. A 1012 mb low near 09N39W is associated with this wave. Scattered moderate convection is evident from 05N to 17N between 37W and 45W. Latest scatterometer and altimetry data show moderate to fresh with locally strong S to SE winds and seas at 5 to 6 ft to the SE of the low. Refer to the Special Features section above for more information on development potential of this low.

A Caribbean tropical wave is near 82W from 19N southward to central Panama, and moving west near 10 kt. Isolated thunderstorms are found over the SW Caribbean Basin.

Another tropical wave is along 91W from near the Mexico-Guatemala border southward into the E Pacific Ocean. Numerous heavy showers and scattered thunderstorms are flaring up across the SE Bay of Campeche, Guatemala and SE Mexico.


A monsoon trough extends across the coast of Guinea-Bissau near 11N16W through a low near 11N20W to 07N45W. No ITCZ is found based on the latest analysis. Scattered moderate to isolated strong convection is present near the low from 10N to 13N between 19W and 24W. Scattered moderate convection is seen S of the monsoon trough from 04N to 10N between 20W and 29W.


For information on Post Tropical Cyclone Nicholas over SW Louisiana, and associated convection in the Gulf, refer to the Special Features section above.

Modest convergent SSE to SW winds are coupling with upper-level winds shear to trigger scattered showers and isolated thunderstorms over the E Gulf, including the Florida Keys and W coast. Please read the Tropical Waves section for additional convection in the Bay of Campeche. Moderate SE trades and seas of 3 to 5 ft are seen N of the Yucatan Peninsula and over the Yucatan Channel. Otherwise, light to gentle variable winds and seas near 2 ft dominate the remainder basin.

For the forecast, Post-Tropical Cyclone Nicholas is drifting northward away from the coast and into the interior of central Louisiana, leaving a gentle winds and mostly slight seas across the Gulf through the next several days.


Convergent trade winds are producing scattered showers and isolated thunderstorms over W Hispaniola and adjacent waters. Refer to the Tropical Waves section above for additional convection across the Caribbean Basin. Moderate to fresh trades and seas at 5 to 7 ft are present over the central and S central basin. Gentle to moderate trades and seas of 2 to 4 ft prevail for the rest of the basin.

For the forecast, the Atlantic ridge will build into the Caribbean through late Sat, supporting fresh to strong winds over the south-central Caribbean and over the Gulf of Honduras through late Sat. The ridge will weaken starting Sun as an area of low pressure currently well east of the area moves to the northeast of the Leeward Islands early next week. There is a medium chance this low pressure will form into a tropical cyclone over the next couple of days. Regardless of further development, expect increase winds, seas and thunderstorms east of the Leewards early next week.


Convergent fresh to strong S to SW winds feeding toward a low pressure system off the S Carolina coast are generating numerous heavy showers and isolated thunderstorms W of Bermuda, N of 30N between 66W and 71W. Seas near this area range from 6 to 9 ft. More information on this low can be found in the Special Features section above. Enhanced by an upper-level trough in the vicinity, a surface trough near 28N52W is causing scattered to numerous moderate convection N of 27N between 45W and 53W. Another surface trough farther SE near 24N44W is creating scattered moderate convection from 24N to 27N between 42W and 46W. Convergent SW winds near a surface trough across S Georgia are triggering scattered showers and isolated thunderstorms off the N Florida- Georgia coast. Refer to the Special Features, Tropical Waves and Monsoon Trough/ITCZ sections for additional convection and sea conditions across the Atlantic Basin.

The Atlantic ridge extending west-southwestward from the 1029 mb Azores high, passing S of Bermuda to the Bahamas continues to dominate the basin. Other than the areas related to the systems in the Special Sections, light to gentle trades and seas at 4 to 5 ft are seen N of 16N between 46W and the Florida coast and the Greater Antilles; gentle to moderate SSE to SW winds and seas of 4 to 6 ft are present S of 13N between the African coast and the Windward Island/S American coast. Moderate to locally fresh NE trades and seas at 6 to 9 ft prevail elsewhere, including waters near the Canary and Cabo Verde Islands.

For the forecast W of 45W, weak ridging across through the central Bahamas will support mostly light breezes and slight seas north of 22N through early next week, and moderate trade winds and moderate seas south of 22N at least through Sat. Meanwhile, an area of low pressure currently well to the southeast over the tropical Atlantic will approach the waters northeast of the Leeward Islands Sun and Mon. There is a medium chance this low pressure will form into a tropical cyclone over the next couple of days. Regardless of development, expect increased winds, seas, and thunderstorms northeast of the Leeward Islands Sun into Mon.