AXNT20 KNHC 271716

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
116 PM EDT Thu Jul 27 2017

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 1800 UTC.


An eastern Atlantic tropical wave extends along 31W from 04N to 17, moving west at 10 kt. Scattered moderate convection is noted from 07N to 12N between 30W and 35W. An 11Z scatterometer pass indicated sharp cyclonic turning at the intersection of the tropical wave and the monsoon trough near 09.5N31W, with winds near 20 kt on the south side of the monsoon trough. Satellite imagery also shows Saharan dust in wrapping into the northern side of the elongated circulation, contrasting with deep layer moisture showing up south of 12N.

A central Atlantic tropical wave extends along 42W from 03N to 16N moving west at 10 to 15 kt. No significant convection is associated with this tropical wave other than a few showers where it intersects the monsoon trough near 09N42W. This is due in part to remnant dry Saharan air with the tropical wave, but also due to subsident dry air in northerly flow aloft.

A tropical wave is along 59W/60W from 12N to 23N moving toward the Lesser Antilles at 15 to 20 kt. The tropical wave is interacting with an upper low centered near 26N58W, and is much better represented north of 18N as a result. The only convection is noted closer to the upper low, from 19N to 22N between 55W and 60W. The tropical wave will move into the eastern Caribbean tonight, followed by moderate to fresh trade winds and a few showers.

A Caribbean tropical wave extends between Haiti and northeast Colombia moving west at 15 to 20 kt. The tropical wave is moving toward an upper low centered over central Cuba, and will start interacting with the upper low through tonight, complicating precise position analysis. No significant convection is associated with the tropical wave, but its presence has allowed the pressure gradient to relax and subsequently diminished the area of strong trade winds across the central Caribbean. This wave will move across the rest of the Caribbean through tonight, and across the western Caribbean Sea Friday through Saturday.


The monsoon trough axis extends from 13N17W to 09N42W, where it transitions to the intertropical convergence zone which reaches to near Trinidad. No significant convection is noted other than what was already mentioned in the tropical wave section above.



Weak ridging extends from central Florida to the Texas coast. A trough is digging into north Florida, supporting scattered showers and thunderstorms over the Big Bend area this morning. Another line of showers and thunderstorms is observed from 26N83W to 24N90W, attributed to divergent flow aloft between an upper low over central Cuba and an upper anticyclone farther north. A similar configuration is supporting scattered moderate to isolated strong convection off Veracruz in the southwest Gulf. The light to gentle winds across the region are maintaining slight seas overall. Little change is expected through Saturday for the majority of the Gulf. On Saturday, a weak front is forecast to drop south over the southeastern United States to near the Florida panhandle by late Saturday may bring an increase of moisture along with an increase in shower and thunderstorm activity to the NE Gulf at that time.


Scattered showers and thunderstorms are diminishing over the northern Caribbean north of 18N to the coast of Cuba, on the periphery of an upper low centered over central Cuba. A large cluster of convection is noted along the coast of Nicaragua, on the southwest quadrant of an weak upper jet south of the upper low. A few showers are noted across the Windward and Leeward Islands moving into the eastern Caribbean, ahead of the tropical wave moving into the region. Ridging north of the area continues to support fresh to locally strong trade across the Caribbean to the S of 17N and E of 82W, with the strongest winds along the coasts of northwest Venezuela and northeast Colombia, with the area of strong winds extending as far north as 15N.


Daytime heating is supporting scattered showers and thunderstorms starting to form over the higher terrain of the island, on the eastern edge of an upper low centered over central Cuba. Moisture is expected to decrease on Friday and Friday night, then increase on Saturday as another tropical wave passes through the central Caribbean Sea.


The main weather maker in the western Atlantic continues to be the upper low centered near 26N58W. As discussed in the tropical wave section above, scattered showers and thunderstorms are active south of the upper low from 19N to 22N between 55W and 60W due to convergent trade winds in the lower levels and upper divergence. Scattered showers and thunderstorms are also ongoing off northeast Florida, south of a stationary frontal boundary situated just to the north off the Carolina coast. Scattered showers are starting to develop across the Bahamas, on the periphery of an upper low centered over Cuba. Weak surface ridging along 28N is supporting light to gentle breezes and slight seas. Farther east, outside areas already discussed in the tropical wave and monsoon trough/ITCZ sections, high pressure over the central Atlantic is maintaining gentle to moderate trade winds, with Saharan dust dominating east of 35W.

For additional information please visit http://www.hurricanes.gov/marine

$$ Christensen