For the North Atlantic, Caribbean Sea and the Gulf of Mexico:
Special Tropical Weather Outlook issued to discuss the potential for subtropical development this week over the central Atlantic.
A large area of low pressure located over the central subtropical Atlantic about 750 miles northeast of the northern Leeward Islands is producing disorganized showers and thunderstorms. Environmental conditions appear conducive for this system to acquire some subtropical characteristics while it drifts northeastward during the next few days. By Thursday night or Friday, however, the low is expected to move over cooler waters, ending its chances of becoming a subtropical cyclone. Additional information on this system, including gale warnings, can be found in High Seas Forecasts issued by the National Weather Service. The next Special Tropical Weather Outlook on this system will be issued by 9 PM EST today or earlier. * Formation chance through 48 hours, low, 30 percent. * Formation chance through 5 days, medium, 40 percent.
High Seas Forecasts issued by the National Weather Service can be found under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php
Posted 11 hours ago by NHC Forecaster Forecaster Cangialosi/Pasch
Atlantic Storm Warning: A deepening broad 1002 mb low is centered near 25N57W. A trough extends from the low to just north of the British Virgin Islands. A stationary front extends from the low northeastward to 27N55W and eastward to 27N50W to 26N43W, and northeastward from there to low pressure near 29N32W 1007 mb. An ASCAT data pass from this afternoon depicted gale- force northeast to east winds within about 300 nm NE of the 1002 mb low. Seas with these winds are in the 14-18 ft range. The low is embedded also within a broad upper-level trough that is clearly evident in water vapor imagery. Latest satellite imagery shows quite an extensive area of numerous moderate convection that covers the area from 20N to 31N and between 42W-58W. This area of convection is gradually sliding east-northeastward. The area of gale-force winds is forecast to expand to north of 27N and between 47W-60W by early on Tue, with seas building to 15-22 ft. Sustained winds in the range of 40-50 kt are forecast to begin late Tue night into early Wed morning. Seas are forecast to significantly build to a range of 24-28 ft by this time. Marine conditions will become substantially hazardous in this region as the low intensifies. Mariners are urged to activate a plan of avoidance to avoid these hazardous conditions. Please read the latest High Seas Forecast issued by the National Hurricane Center at the website: http://www.nhc.noaa.gov/text/MIAHSFAT2.shtml for more details.
The monsoon trough axis approaches the coast of Sierra Leone, but remains inland over Africa. Latest scatterometer data indicates that the ITCZ begins just offshore the coast of Sierra Leone near 07N12W and extends to 06N24W, and resumes to the west of a trough near 06N27W to 07N36W to 06N43W and to 06N50W. Scattered moderate to isolated strong convection is noted within 180 nm north of the ITCZ between 19W-24W. Scattered moderate convection is within 240 nm south of the ITCZ between 18W-22W, within 60 nm south of the ITCZ between 31W-35W and within 60 nm north of the ITCZ between 36W-45W.
Gulf Of Mexico
The 18 UTC analysis has a 1019 mb high center over the far eastern Gulf near 27N83W. A 1019 mb high center is just inland the coast of Mexico near Jalapa. Generally, weak high pressure is present over the area. The associated gradient is allowing for gentle to moderate southeast to south winds over the area, except in the southeastern part of the Gulf, including the Straits of Florida, where winds are from the east, gentle to moderate in speeds. Seas are 3-5 ft throughout, with the exceptions of the north- central, northeast and southeastern sections, where seas are slightly lower in the 2-4 ft range per latest buoy observations and altimeter data passes. The basin remains void of significant convection, with the exception of a few thunderstorms over the central Bay of Campeche. This activity will most likely dissipate in a few hours. Broken areas of dense fog are over the coastal waters of southeastern Louisiana, Alabama and northwest Florida.
For the forecast, high pressure over the area will remain in place through Fri. Moderate to fresh return flow will continue west of 92W through Wed.
The pressure gradient between high pressure over the Gulf of Mexico and lower pressures western Caribbean and over Colombia is allowing for fresh to strong north to northeast winds south of Cuba and Hispaniola, including the Windward and Mona Passages, where seas are 6-8 ft. Elsewhere, latest satellite ASCAT data passes indicate moderate trade winds over the eastern Caribbean where seas are 3-5 ft, and moderate to fresh trade winds are over the western and northwestern Caribbean Sea, where seas are 4-6 ft. Moderate to fresh trade northeast to east trade winds are also noted within 60 nm of the coast of Colombia, also with seas of 4-6 ft.
For the forecast, deepening low pressure across the central Atlantic during the next few days will initiate northeast winds across much of the basin, and fresh to locally strong north to northeast winds through the Caribbean Passages and in the lee of Cuba through Thu. Large northeast swell in the central Atlantic will move through the Caribbean Passages and Tropical Atlantic waters through the end of the week.
Please read the Special Features section above for information about ongoing gale winds that are forecast to increase to storm force in association with deepening broad low pressure that is centered about 530 nm southeast of Bermuda.
The dominate feature in the Atlantic basin is the Special Features 1002 mb deepening low pressure system that is centered near 25N57W. A surface trough extends from this system southwestward to just north of the British Virgin Islands. Isolated showers are along and the trough. These showers are moving in a general north to south motion per satellite imagery detected motion, and as seen on the San Juan radar display imagery. Moderate to fresh northwest to north winds are west of the trough to near 62W. Similar winds are within 180 nm east of the trough from 22N to 24N. Moderate to fresh north winds are elsewhere west of the low and trough to near 73W. Light to gentle north to northeast winds are west of 73W, except for northeast to east south of 25N and west of the Bahamas, including the Straits of Florida. Large seas are in the range of 6-9 ft primarily due to a long-period northeast swell elsewhere west of the low and trough to the Bahamas and to 78W north of Bahamas. Seas are 5-7 ft west of the Bahamas and 78W, except 3-5 ft in the Straits of Florida. The remainder of the central and eastern Atlantic is dominated by high pressure, with 1016 mb high center near 23N22W. The associated gradient is allowing for gentle to moderate anticyclonic winds over these sections of the discussion area.
For the forecast W of 55W, fresh to strong north to northeast winds will continue east 70W through late Tue associated with the 1002 mb low pressure system near 25N57W. The low will move in a small cyclonic loop and deepen through Wed, before moving northeast to east, then exit the region to the northeast on Fri. Near gale force winds are occurring across the far northeastern waters will increase to gale-force tonight, then briefly to storm force by Wed morning. Winds will then diminish slightly with gale- force winds continuing Wed afternoon through Thu. Large long- period north to northeast swell will continue to impact the Atlantic waters and Caribbean Passages between the southeastern Bahamas and the eastern Caribbean, with high seas throughout the rest of the week. Large east swell is forecast to reach the Florida offshore waters north of 26N from early Fri through Sat.
Posted 1 hour, 8 minutes ago by NHC Forecaster Aguirre