AXPZ20 KNHC 212115

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 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 1800 UTC surface analysis and satellite imagery through 2115 UTC.


Tropical Storm Greg is centered near 14.9N 120.7W, or 780 nm SW of the southern tip of the Baja Peninsula at 21/2100 UTC, moving WNW at 11 kt. Estimated minimum central pressure is 1003 mb. Maximum sustained winds have decreased to 45 kt with gusts to 55 kt. Visible satellite imagery shows the well defined low level center becoming completely exposed this afternoon with convection displaced from the center. Scattered moderate to strong convection is noted within 120 nm in the NE quadrant of the center. Greg is forecast to begin slowly intensifying on Sat with peak intensity expected to remain below hurricane strength on Sun. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP2 WTPZ22 for more details.

Tropical Depression Nine-E is centered near 9.0N 94.7W, or about 420 nm SSE of Puerto Angel, Mexico, moving W at 12 kt. Estimated minimum central pressure is 1008 mb. Maximum sustained winds are 30 kt with gusts to 40 kt. Scattered moderate to strong convection was observed in banding features within 120 in the NW and 60 nm in the SE semicircles of the center. An additional area of strong convection was noted from 11.5N to 13N between 95W and 97W. Environmental conditions are favorable for additional strengthening and the system could become a tropical storm later overnight. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP4 WTPZ24 for more details.

A 1008 mb surface low continues near 14N110W in association with a tropical wave along 110W/111W. Scattered moderate to strong convection is confined to within 180 nm in the W semicircle of the low due to the presence of persistent northeasterly shear. Environmental conditions are favorable for tropical cyclone formation as this low continues NW to near 15N113W Sat and near 16N116W by Sun.


The monsoon trough extends from the coast of Colombia at 08N78W to the coast of Costa Rica at 10N85W to 09N91W. The monsoon trough breaks down in the vicinity of newly formed T.D. Nine-E and a surface low near 14N110W, then resumes from 14N120W to the remnant low of T.D. Eight-E near 12N127W to 12N131W. The ITCZ extends from 12N131W to 10N140W. Scattered moderate convection was noted within 120 nm in the S quadrant of the low near 12N 127W.



Gentle to moderate NW winds off the Baja California peninsula are expected to continue through Sat. Seas will remain 5 to 7 ft in a mix of long period north and southwesterly swell. Gentle southerly flow will persist in the Gulf of California, except for moderate southerly flow over the northern Gulf.

Strong northerly gap winds of 20-25 kt are expected to pulse through the Gulf of Tehuantepec overnight into Sat morning toward developing T.D. Nine-E. Seas will build to 8 ft with an additional component of longer period southwest swell.


In the Gulf of Papagayo, moderate to fresh offshore winds will pulse to fresh each night with nocturnal drainage through the week, occasionally building max seas to 8 ft in a mix of east swell and longer period southwest swell.

Gentle to 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.

REMAINDER OF THE AREA... The remnant low of TD 8-E is analyzed near 12N128W and estimated pressure of 1011 MB, with fresh to strong winds continuing within 120 nm of the center. The low will gradually dissipate through Sat.

The pressure gradient between Fernanda and Greg and high pressure to the N of the area 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.

$$ Cobb