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AXPZ20 KNHC 211515
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1605 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 1200 UTC surface analysis and satellite imagery through 1515 UTC.


...SPECIAL FEATURES...

Tropical Storm Greg is centered near 15.1N 119.2W, or 700 nm SW of the southern tip of the Baja Peninsula at 21/1500 UTC, moving WNW at 9 kt. Estimated minimum central pressure is 1001 mb. Maximum sustained winds are now 50 kt with gusts to 60 kt. Scattered moderate to strong convection is noted within 90 nm in the NW and 45 nm in the SE semicircles of the center. Greg is forecast to slowly intensify and reach hurricane strength in 36 to 48 hours. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP2 WTPZ22 for more details.

Newly formed Tropical Depression Nine-E is centered near 9.0N 93.5W, or about 440 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 a large banding feature within 120 to 150 nm in the SE semicircle and 180 nm in the W quadrant of the depression. Environmental conditions are favorable for additional strengthening and the system could become a tropical storm later today. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP4 WTPZ24 for more details.

A 1008 mb surface low continues near 13N109W in association with a tropical wave along 109W/110W. Scattered strong convection is confined to within 180 nm in the SW quadrant of the low due to the presence of northeasterly shear. The pressure gradient is supporting strong winds within 240 nm of the low. Environmental conditions are favorable for tropical cyclone formation as this low continues NW to near 14N112W early Sat and near 15N114W early Sun.


...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

The monsoon trough extends from the coast of Colombia at 08N78W to the coast of Costa Rica at 09N85W, to the vicinity of newly formed T.D. Nine-E near 08N95W to 12N100W to another surface low at 13N109W to 14N112W, then resumes from 13N120W to the remnant low of T.D. Eight-E near 12N127W to 12N130W. The ITCZ extends from 12N130W to 10N140W. Except noted with the systems described above, minimal convection is associated with the trough axis.


...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

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 to near gale force northerly gap winds pulsed through the Gulf of Tehuantepec this morning toward developing T.D. Nine-E. Winds will once again pulse tonight and early Sat but only to 20- 25 kt. Seas will build to 8 ft with an additional component of longer period southwest swell.

OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR...

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...

Tropical Storm Fernanda has moved further W of 140W with winds and seas diminishing to 20-25 kt and 8-9 ft from 19N-22N west of 135W. The residual effects of Fernanda will shift W of 140W by this evening.

The remnant low of TD 8-E is analyzed near 12N127W and estimated pressure of 1010 MB, with fresh to strong winds continuing within 120 nm of the center. The low will gradually dissipate through tonight.

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

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