AXPZ20 KNHC 201819 CCA

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


Tropical Storm Fernanda is centered near 18.2N 139.2W at 20/1500 UTC moving WNW at 10 kt. Estimated minimum central pressure is 995 mb. Maximum sustained winds are 55 kt with gusts to 65 kt. Scattered moderate to strong convection within 120 nm NE quadrant of center. Fernanda will continue to weaken as it moves west of 140W later today. Large swell will continue to expand and spread out ahead of Fernanda to the NW and W during the next few days. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP1/WTPZ21 for more details.

Tropical Storm Greg is centered near 14.1N 115.4, or 585 nm SSW of the southern tip of the Baja Peninsula at 20/1500 UTC, moving W at 9 kt. Estimated minimum central pressure is 1003 mb. Maximum sustained winds have increased to 45 kt with gusts to 55 kt. Scattered moderate to strong convection is noted within 90 nm of the center, except in the NW quadrant. Greg is forecast to slowly intensify and reach hurricane strength within 48 hours. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP2/WTPZ22 for more details.

Tropical Depression Eight-E is centered near 13.4N 123.1W, or about 890 nm SW of the southern tip of the Baja Peninsula at 20/1500 UTC, moving WSW at 5 kt. Estimated minimum central pressure is 1009 mb. Maximum sustained winds remain 25 kt with gusts to 35 kt. Eight-E is now experiencing southwesterly shear and is not expected to reach tropical storm strength. See the latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP3/WTPZ23 for more details.

A tropical wave is analyzed from 06N to 19N along 104W. A surface low is embedded in the wave near 12N104W with an estimated pressure of 1010 mb. An overnight scatterometer satellite pass indicated fresh to strong winds within 180 nm to 240 nm of the center in the northeast quadrant. The low pressure may become a tropical cyclone as continues to the WNW with the wave at 10 to 15 kt over the next couple of days. Scattered moderate isolated strong convection observed from 07N to 12N between 104W and 110W, mainly along the monsoon trough. An additional area of scattered moderate to strong convection was noted within 120 nm of the coast of Mexico between 100W and 106W.


The monsoon trough extends from 08N78W to low pressure 1010 mb near 08N86W to the developing low pressure 1010 mb near 11N104W, where the monsoon trough loses definition near T.S. Greg. 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 the monsoon trough between 87W and 94W.



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.


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.


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, with seas 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