000 AXNT20 KNHC 031755 TWDAT Tropical Weather Discussion NWS National Hurricane Center Miami FL 155 PM EDT Thu Sep 3 2020 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 32N. The following information is based on satellite imagery, weather observations, radar and meteorological analysis. Based on 1200 UTC surface analysis and satellite imagery through 1715 UTC. ...SPECIAL FEATURES... Tropical Storm Nana is centered near 16.4N 90.3W at 03/1500 UTC or 110 nm N of Guatemala City Guatemala moving W at 13 kt. Estimated minimum central pressure is 1004 mb. Maximum sustained wind speed is 40 kt with gusts to 50 kt. On the forecast track, the center of Nana will move over northern Guatemala and southeastern Mexico today and tonight, then move over the Gulf of Tehuantepec on Friday. Continued rapid weakening is forecast, and Nana will likely become a remnant low on Friday. Nana is forecast to produce rainfall amounts of 3 to 6 inches, isolated totals of 8 inches over central and western Guatemala and the Mexican state of Chiapas. These rainfall amounts may produce life threatening flash floods and mudslides. Swells generated by Nana affecting portions of the coasts of northwestern Caribbean Sea should subside today. Please consult products from your local weather office. Please read the latest NHC Public Advisory at https://www.nhc.noaa.gov/text/MIATCPAT1.shtml and Forecast/ Advisory at https://www.nhc.noaa.gov/text/MIATCMAT1.shtml for more details. Tropical Depression Omar is centered near 35.9N 61.1W at 03/1500 UTC or 290 nm NE of Bermuda moving E at 11 kt, and this general motion is expected to continue through Friday morning, accompanied by a slight decrease in forward speed. A turn toward the east-northeast and northeast is expected Friday and Friday night. Estimated minimum central pressure is 1005 mb. Maximum sustained wind speed is 30 kt with gusts to 40 kt. The center of Omar is currently exposed due to fairly strong WNW shear impacting the system. An area of moderate convection is seen to the SE of the center. Gradual weakening is forecast, and Omar is expected to become a remnant low on Friday, or possibly sooner. The remnant low should dissipate on Saturday. Please read the latest NHC Public Advisory at https://www.nhc.noaa.gov/text/MIATCPAT5.shtml and Forecast/ Advisory at https://www.nhc.noaa.gov/text/MIATCMAT5.shtml for more details. ...TROPICAL WAVES... A tropical wave that has emerged off the west coast of Africa is along 18N, from 18N southward. A 1008 mb low pressure is analyzed along the wave axis near 14N. The low pressure is well defined on visible satellite imagery, and scatterometer data show fresh SW winds on the SE quadrant of the low center. This system is producing a large area of scattered moderate convection from 10N- 15N between 16W-22W. This wave is merging with another disturbance located a couple of hundred miles south of the Cabo Verde Islands. Development of this system is likely to be slow during the next couple of days while it moves west-northwestward at about 10-15 kt. After that, a tropical depression is more likely to form early next week over the central tropical Atlantic where environmental conditions are forecast to be more favorable for development. The latest Tropical Weather Outlook states that this system has a high chance of tropical cyclone formation through 5 days. Refer to the latest Tropical Weather Outlook at www.hurricanes.gov for more details. A tropical wave is along 25W, from 18N southward, moving westward 10 to 15 knots. A 1008 mb low pressure is along the wave axis near 12N. Scattered moderate to isolated strong convection is observed mainly to the west of the low center from 11N-13N between 22W- 27W. This system has a low chance of tropical cyclone formation within the next 48 hours, but a high chance that a tropical depression will form through the next five days. Refer to the latest Tropical Weather Outlook at www.hurricanes.gov for more details. Another tropical wave is analyzed along 43W/44W S of 18N based on Tropical Wave Diagnostic. A swirl of low clouds is noted near the northern end of the wave axis. A tropical wave is along 57W from 19N southward. Visible satellite imagery shows a well defined inverted-V pattern associated with the wave. Some shower activity is noted near the wave axis but mainly from 12N-16N. Moisture related to this wave will spread over the Lesser Antilles tonight into Fri, increasing the likelihood of showers and isolated tstms. Barbados is already reporting some shower activity. A tropical wave is over the Caribbean Sea along 77W/78W from Jamaica southward, moving W 10 to 15 knots. Scattered moderate to isolated strong convection is observed from 13N-18N between 75W-81W. ...MONSOON TROUGH/ITCZ... The monsoon trough passes through the southern coastal sections of Mauritania to 14N18W to 12N25W to 12N41W. A large monsoonal circulation is noted between the W coast of Africa and roughly 40W. Three low pressure systems of 1008 mb are noted along the monsoon trough. Two of them are mentioned in the Tropical Wave section above. The third one is near 12.5N37W. Scattered moderate convection is within about 90 nm NW quadrant of low center. Most of the convection is associated with the tropical waves and low pressure systems. GULF OF MEXICO... A ridge, extending from the Atlantic Ocean, dominates the Gulf waters. A 1017 mb high pressure is over the NE Gulf near 28N87W. Recent satellite-derived wind data show moderate to locally fresh E-SE winds over the SE Gulf between the ridge to the north and T.S. Nana over Guatemala. Gentle to moderate winds are elsewhere, with the exception of light and variable winds over the NE Gulf due to the presence of the high center. An area of showers and thunderstorms is noted near Veracruz. A few showers are active over the south central Gulf related in part to low level convergence in the easterly flow, and a diffluent pattern aloft. The high pressure over the northeastern Gulf will dissipate through Fri ahead of a weak front moving into the northern Gulf Sat. The front will stall over the northern Gulf Sun, then slowly dissipate through early next week. Looking ahead, another stronger cold front may enter the northwest Gulf by mid week. CARIBBEAN SEA... Please see the Special Features section above for information on T.S. Nana. A moist pattern prevails across the Caribbean in the wake of Nana. Satellite-derived precipitable water values show very high deep layer moisture over most of the basin. Clusters of showers and thunderstorms are observed in a large swath from the Lesser Antilles all the way to the NW Caribbean, including the Yucatan Channel. An upper-level low spinning over Puerto Rico is also supporting the convective activity over the eastern Caribbean. The San Juan Doppler Radar currently shows an area of scattered showers and thunderstorms over western Puerto Rico. Similar convective activity is also noted across the regional waters. Recent scatterometer data provide observations of fresh easterly winds in the wake of the tropical wave located along 77W/78W. These winds are affecting mainly the waters from 16N-18N between 70W-77W. Fresh NE winds are also noted over the Windward Passage. Winds are light and variable over the south-central Caribbean, including the Colombia basin. The usual trade wind pattern has been temporarily interrupted due to the passage of Nana. The Caribbean will gradually revert back to its normal pattern over the next several days with moderate to fresh trade winds mainly over the central part of the basin. ATLANTIC OCEAN... A weak surface ridge extends east to west across the waters north of 25N. This is supporting light and variables winds N of 25N, with gentle to moderate winds along the southern periphery of the ridge. Pulses of fresh to strong winds are possible north of Hispaniola and near the Windward Passage tonight. The ridge will dissipate by Sun ahead of a weak frontal boundary entering the area from the north, but otherwise little change is expected into early next week W of 65W. Farther east, fresh to locally strong SW winds and 8 to 9 ft seas are south of the monsoon trough mainly east of 35W. As previously mentioned, the monsoon trough is very active over the eastern tropical Atlantic, and there is a high chance a tropical depression will form in the eastern or central tropical Atlantic by early next week. $$ GR