AXNT20 KNHC 211204

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
804 AM EDT Sat Jul 21 2018

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 0600 UTC surface analysis and satellite imagery through 1130 UTC.


A tropical wave is in the E Atlc with axis extending from 05N-18N along 30W, moving W at 10-15 kt. Saharan dry air and dust continue to prevail in the wave's environment as shown by CIRA LPW and GOES-16 RGBs imagery. This is inhibiting convection at this time.

A tropical wave is in the central Atlantic with axis extending from 05N-21N along 47W, moving W at 10-15 kt. The wave is moving across an extensive area of Saharan dry air, which is hindering convection at the time.

A low amplitude and low latitude tropical wave is moving across Venezuela into eastern Colombia with axis extending from 00N-10N along 67W, moving W at 10-15 kt. Scattered moderate convection is observed over the mountains of southern Venezuela between 65W- 68W. This wave is forecast to move into the Eastern Pacific waters on Mon.

A tropical wave is in the west-central Caribbean with axis along 82W, moving W at 15-20 kt. Scattered showers are noted along the wave's axis in the vicinity of the monsoon trough mainly south of 12N.


The monsoon trough axis extends from the coast of Mauritania in W Africa near 19N16W and continues to 09N25W to 08N45W. The ITCZ begins near 07N50W and continues to South America near 07N59W. No significant convection is observed along these boundaries at this time.



A surface trough continues over the far northeast Gulf waters in the Big Bend area of Florida, supported by a mid- level trough that extends over the eastern U.S., which also supports a dying stationary frontal system north of the area. Scattered showers and a few thunderstorms are noted south of the trough in the eastern Gulf from 26N to 28N between 83W and 85W. Elsewhere, the remainder Gulf is under the influence of a surface ridge, anchored by a 1016 mb high centered near 27N90W. This is providing light to moderate anticyclonic winds across the basin. The trough is forecast to lift NE of the area this morning and surface ridging will prevail thereafter through the weekend. A surface trough will move off the Yucatan Peninsula into the Bay of Campeche each evening, accompanied by fresh nocturnal winds and scattered showers. Another surface trough will move into the NE gulf early next week. A surface trough will move off the Yucatan Peninsula into the Bay of Campeche each evening, accompanied by fresh nocturnal winds. Otherwise little change is expected.


The majority of the basin is pretty quiet as very dry air prevails across the area. A tropical wave is moving across the western Caribbean, however lacks convection due to the aforementioned conditions. The only region of convection is within 150 nm off the coast of Costa Rica and northern Panama where the eastern Pacific monsoon flow supports scattered showers and tstms. For more information about the wave, refer to the section above. A scatterometer pass from several hours ago confirmed fresh to strong trade winds off the coast of northeast Colombia. A concurrent altimeter pass showed seas to 8 ft, although seas are likely a little higher farther west off the central coast of Colombia due to a greater fetch of fresh to strong trade winds. Strong to near-gale force winds and associated higher seas are forecast to persist through tonight before winds diminish. No major changes expected through early next week.


Mid to upper-level diffluent flow between a ridge in the west Atlantic and a trough along the eastern U.S. continue to support scattered showers and tstms in a line from roughly Grand Bahama to north of 31N75W. Similarly divergent flow aloft between the upper ridge and an upper low farther east near 28N57W will support scattered showers and thunderstorms northeast of the Turks and Caicos Islands within 90 nm of of 24N69W. Fair weather is elsewhere, however hazy conditions are expected S of 26N as an extensive Saharan Air Layer outbreak moves across the Atlantic tropical waters.

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

$$ Christensen/ERA