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000
AXPZ20 KNHC 202114
TWDEP

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 UTC Thu Jul 20 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.


...SPECIAL FEATURES...

Tropical Storm Fernanda is centered near 18.2N 140.4W at 20/2100 UTC moving W at 11 kt. Estimated minimum central pressure is 998 mb. Maximum sustained winds are 50 kt with gusts to 60 kt. There is no deep convection associated with Fernanda, however the system still remains well organized with the edge of an 1850 UTC ASCAT pass still showing tropical storm force winds in the W semicircle. Fernanda will continue to weaken as it moves further W of the area tonight and Friday. This is the last advisory being issued by the National Hurricane Center on this system. Forecast/advisories will be issued by the Central Pacific Hurricane Center under AWIPS/WMO headers HFOTCMCP1/WTPA21 PHFO.

Tropical Storm Greg is centered near 14.2N 116.4, or 640 nm SSW of the southern tip of the Baja Peninsula at 20/2100 UTC, moving W 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 180 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.

Tropical Depression Eight-E has degenerated into a post-tropical remnant low as of 20/2100 UTC. The low is centered near 13.3N 123.9W, or about 980 nm WSW of the southern tip of the Baja Peninsula, moving WSW at 6 kt. Estimated minimum central pressure is 1009 mb. This is the last advisory issued on this system. Additional information on the remnant low can be found please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC.

A tropical wave is analyzed from 06N to 19N along 105W/106W. A surface low is embedded in the wave near 12N106W with an estimated pressure of 1008 mb. A 1710 UTC ASCAT scatterometer satellite pass indicated fresh to strong winds within 180 nm to 240 nm of the center in the N quadrant. The low pressure has a high probability of becoming a tropical cyclone as it continues to move WNW with the wave at 10 to 15 kt over the next couple of days. Scattered strong convection was observed within 180 nm in the W semicircle of the low. An additional area of scattered moderate to strong convection was noted within 60 to 90 nm of 15N103.5W.


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

The monsoon trough extends from 09N84W to low pressure 1010 mb near 08N87W to the developing low pressure 1008 mb near 12N106W, where the monsoon trough loses definition to the southeast of T.S. Greg near 12N100W. The intertropical convergence zone is west of the area. Other than convection already discussed above, scattered to moderate convection is noted within 120 nm either side of line from 06N88W to 10N96W to 11N103W.


...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

Please see the special features for information on Tropical Storm Greg southwest of Manzanillo, Mexico.

The weak trough west of the the Baja California peninsula has dissipated and has allowed the subtropical ridge to advance to the east. However, gentle to moderate NW winds off the Baja California peninsula are expected to continue through Fri. 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.

Fresh to strong northerly gap winds will once again pulse to around 20 kt during mainly overnight and early morning hours through early Friday, with a shorter pulse of strong gap winds again Friday night into Saturday. 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...

Please see the special features section for information on T.S. Fernanda and Tropical Depression Eight-E.

The pressure gradient between Fernanda, and eventually the approaching Greg, will maintaining moderate to fresh northeast winds north of 25N and W of 127W, with seas of 5 to 8 ft including components of northerly swell mixing with southerly swell emerging from Fernanda. Looking ahead, northerly swell to 8 ft will propagate south of 32N and west of 120W.

$$ Cobb

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