AXPZ20 KNHC 210236

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0405 UTC Fri Jul 21 2017

Tropical Weather Discussion for the eastern Pacific Ocean from the Equator to 32N, east of 140W. The following information is based on satellite imagery, weather observations, radar, and meteorological analysis.

Based on 0000 UTC surface analysis and satellite imagery through 0215 UTC.


Tropical Storm Greg is centered near 14.3N 117.4W, or 770 sm SW of the southern tip of the Baja Peninsula at 0300 UTC 21 JUL, moving W or 275 deg at 9 kt. Estimated minimum central pressure is 1003 mb. Maximum sustained winds are 45 kt with gusts to 55 kt. Scattered moderate to strong convection is noted within 150 nm of the center. Greg is forecast to slowly intensify and reach hurricane strength within 36 to 48 hours. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP2 WTPZ22 for more details.

A 1009 mb surface low developed along a tropical wave near 08N90W with scattered moderate isolated strong convection observed within 210 nm over the SE quadrant and over the W semicircle of center. Environmental conditions are favorable for this low to strengthen to a tropical cyclone reaching near 10N94W late Fri and near 12N107W late Sat.

A 1008 mb surface low continues near 12N107W in association with a tropical wave along 108W. Currently, scattered strong convection is noted W of the low within 120 nm of 12.5N109W. The pressure gradient is supporting strong to near gale force winds within 240 nm over the NE quadrant of the low. Environmental conditions are favorable for tropical cyclone formation as this this low continues NW to near 14N111W late Fri and near 15N113.5W late Sat.


The monsoon trough extends from the coast of Colombia at 09N78W to the coast of Costa Rica at 11N86W, then turns SW through a surafce low at 08N89W, then turns NW to another surface low at 12N107W where it loses identity. Other than convection already discussed above, scattered moderate isolated strong convection is noted within 90 nm of 08N96W and 14N122W.



A NW to SE orientated ridge extends into the area from 23N116W to 18N105W supporting gentle to moderate NW winds W of the Baja California Peninsula, with combined seas of 5-7 ft in a mix of long period NW and SW swell. Gentle southerly flow will persist in the Gulf of California, except for moderate southerly flow occasionaly over the northern Gulf.

Fresh northerly gap winds expected in the Gulf of Tehuantepec overnight into the early morning hours Fri. Seas will build to 8 ft, with an additional component of longer period southwest swell.


In the Gulf of Papagayo, moderate to fresh nocturnal offshore winds will continue for the next several days building seas to 8 ft in a mix of the resultant E swell and longer period SW swell.

Moderate southerly winds are expected south of the monsoon trough axis. Long period cross-equatorial southerly swell and 6- 7 ft seas will continue to propagate into the waters reaching the coast of Central America through the day. Another pulse of large southerly swell will move into the region today and raise seas to 6-8 ft through tonight.


Tropical Storm Fernanda has moved W of 140W, however, strong to near gale force winds continue from 17N-23N W OF 137W, with seas of 11-17 FT. Scattered moderate convection is observed within 60 nm of 20N139W. Fresh cyclonic winds and 7-11 ft seas are observed elsewhere W of 135W between 13N-26N. Expect all associated conditions to shift W of 140W on Fri night.

The remnant low of TD 8-E is analyzed near 13N126W and estimated at 1009 MB, with strong winds continuing within 120 nm of the center. The low will gradually dissipate through Fri.

The pressure gradient between Fernanda and Greg will maintain moderate to fresh NE winds N of 25N and W of 127W through the upcoming weekend. Northerly swell in the form of 7-8 ft seas will propagate S of 32N between 125W and 135w early next week.

$$ Nelson