AXNT20 KNHC 171020

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
620 AM EDT Thu Aug 17 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 0600 UTC surface analysis and satellite imagery through 1015 UTC.


Hurricane Gert is centered near 41.7N 54.0W at 17/0900 UTC or about 300 nm S of Cape Race Newfoundland moving ENE at 34 kt. Estimated minimum central pressure is 968 mb. Maximum sustained wind speed is 85 kt with gusts to 105 kt. Numerous moderate convection and scattered tstms are from 40N-44N between 50W-55W. Scattered moderate convection is elsewhere from 40N-48N between 45W-55W and from 35N-39N between 54W-60W. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMAT3/WTNT23 KNHC for more details.

A 1008 mb low is located about 475 nm east of the Lesser Antilles near 13N52W. Intrusion of Saharan dry air and dust to its environment is observed in GOES-16 experimental imagery and CIRA LPW imagery, however the system continue to show signs of organization. This being favored in part by low vertical wind shear. Scattered moderate convection and isolated tstms are within 220 nm W semicircle from low center. Upper-level winds are forecast to become more conducive for development during the next day or so while the low moves westward across the tropical Atlantic Ocean, crossing into the Caribbean Sea on Friday. Regardless of development, locally heavy rainfall and gusty winds are expected to spread across portions of the Lesser Antilles on Thursday night and Friday. This system has a medium chance of becoming a tropical cyclone in the next two days.

A tropical wave is in the central Atlc associated with a 1009 mb low pressure located near 14N40W. The wave axis extends from 21N40W to the low and has been moving W at 15 kt. The wave is in a region of low to moderate vertical wind shear, however intrusion of Saharan dry air and dust to the wave environment limit convection to scattered moderate within 245 nm NW quadrant of low pressure center. Gradual development of this system is possible during the next few days while it moves WNW, but upper-level winds are expected to become less conducive for tropical cyclone formation when the disturbance moves north of the Leeward Islands this weekend. This system has a medium chance of becoming a tropical cyclone in the next two days.


A tropical wave is in the E Atlc associated with a 1010 mb low near 08N21W. The wave axis extends from 16N21W to the low center to 04N21W. The CIRA LPW imagery show dry air intrusion to the wave environment, which has significantly reduced the convection this wave had when it was coming off the W African coast yesterday. GOES-16 experimental and Meteosat SAL imagery show Saharan dust and dry air engulfing this wave. Monsoon moisture and middle to upper level diffluent flow support scattered moderate convection and isolated tstms from 06N to 16N E of 29W. Environmental conditions are forecast to become more conducive for development over the weekend while the system moves WNW.

A tropical wave is in the E Caribbean with axis extending from 21N65W to 11N69W, moving W at 15-20 kt. There is abundant moisture associated with this wave that along with upper level divergent flow support scattered moderate convection and tstms from 16N-24N between 61W-71W, including Puerto Rico.

A tropical wave is in the Yucatan Peninsula with axis extending from 21N87W across Belize and Guatemala to 11N89W, moving W at 20 kt. The wave is in a region of low vertical wind shear, however dry air subsidence continue to limit convection to isolated showers within 90 nm of its axis.


The monsoon trough extends from the African coast near 13N16W to 08N21W to 08N33W. To the west, the monsoon trough and ITCZ is disrupted due to the tropical lows and tropical waves mentioned above. Otherwise, scattered moderate convection is from 04N-09N between 30W-46W.



Except for isolated showers and tstms within 60 nm of Veracruz, Mexico supported by middle level diffluent, the remainder basin in under the influence of a surface ridge anchored by a 1017 mb high near 27N85W. This setup is providing ESE gentle to moderate flow across the Gulf, except for fresh winds off the Texas coast and light to gentle variable flow in the NE basin around the high center. The high is expected to persist across the NE Gulf waters through early Saturday. A surface trough will develop each evening across the Yucatan peninsula shifting W into the Bay of Campeche during the overnight hours. Locally higher winds can be expected in the vicinity of the trough axis.


A tropical wave is moving across the Yucatan Peninsula, Belize and Guatemala supporting isolated showers. A second tropical wave is in the E Caribbean with axis near 68W, which is supporting scattered showers and tstms over the N and NE basin including Puerto Rico, the Virgin Islands and Dominican Republic adjacent waters. See tropical waves section for further details. Generally, diffluent flow is observed in the SW Caribbean, which is supporting numerous heavy showers and tstms from 09N-12N between 80W-84W. Lastly, a diffluent flow pattern persist between an upper level ridge anchored over S Georgia and a low centered N of the Windward Passage. This continue to support isolated showers across central Cuba. Otherwise, dry air subsidence and strong vertical wind shear support fair weather elsewhere W of 70W. Fresh to strong winds in the south-central waters and in the vicinity of the tropical wave in the eastern waters are expected today with moderate to fresh trades elsewhere.


An upper level low is centered N of the Windward Passage ahead of a tropical wave that is forecast move over the central Caribbean later this morning. The approaching wave is already supporting scattered showers and tstms over the Dominican Republic adjacent waters and isolated showers inland, but this activity will increase through the course of the day into Friday.


Except for the SW N Atlc waters that are being impacted by the tropical wave moving to central Caribbean waters later this morning, the remainder basin generally N of 20N is under the influence of the Azores subtropical high which supports fair weather. Otherwise, see special features and tropical waves sections above.

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

$$ Ramos