000 AXPZ20 KNHC 180913 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 912 UTC Tue Jul 18 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 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Hurricane Fernanda is centered near 15.4N 132.8W at 0900 UTC or about 1355 nm WSW of the southern tip of Baja California or about 1345 nm E of Hilo, Hawaii moving NW at 8 kt. Estimated minimum central pressure is 971 mb. Maximum sustained winds remain 90 kt with gusts to 110 kt. Numerous moderate to strong convection is within 90 nm of the center, with scattered moderate to strong convection elsewhere within 240 nm east semicircle and 150 nm west semicircle. Fernanda is weakening, and no longer exhibits an eye. The weakening trend will continue over the next several days. Large swells will continue to expand and spread out ahead of Fernanda to the NW and W during the next few days, and are expected to reach the Hawaiian Islands early Wednesday. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP1/WTPZ21 for more details. Newly formed Tropical Storm Greg near 14.6N 107.6W at 0900 UTC or about 330 nm SSW of Manzanillo, Mexico moving WNW at 8 kt. Estimated minimum central pressure is 1006 mb. Maximum sustained winds are 35 kt with gusts to 45 kt. Scattered moderate to strong convection is within 45 nm in the northwest semicircle and 90 nm in the southeast semicircle. While Greg is intensifying currently, little further intensification is anticipated over the next couple days, with gradual weakening expected by the end of the weak. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP2/WTPZ22 for more details. An area of low pressure centered near 14N118W 1008 mb, or about 720 nm southwest of the southern tip of the Baja California peninsula. Weak northerly shear is ongoing, maintaining scattered moderate to strong convection within 60 nm in the northern semicircle and 180 nm in the southern semicircle. Fresh to strong winds and seas of 7 to 9 ft can be found within 180 nm in the southeast semicircle of the low. The low will continue to move slowly to the west or west-southwest through midweek, and may eventually interact with Tropical Storm Greg. The low has a medium chance for tropical cyclone development during the next 48 hours. ...TROPICAL WAVES... A tropical wave extends north of 10N along roughly 89W/90W through western El Salvador and eastern Guatemala. A squall line related to the tropical wave moved off the coast of Guatemala and El Salvador a few hours ago, bringing strong thunderstorms, gusty winds, and locally higher seas to the adjacent Pacific waters out to 60 nm off the coast. This has largely diminished since however, with a few thunderstorms lingering off the central coast of Guatemala. The tropical wave is moving west at 15 kt. Another tropical wave extends north of 10N along 99W/100W, moving west at 10 to 15 kt. Scattered moderate convection is noted along the monsoon trough near the tropical wave from 07N to 10N between 95W and 100W. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 08N78W TO 11N94W to 09N102W, where it breaks from Tropical Storm Greg, then resumes from 114N112W to low pressure near 14N118W TO 13N125W, where it breaks, then resumes to the southwest of Fernanda near 11N132W to beyond 08N140W. Other than convection as already described, scattered moderate convection is from 06N to 08N between 135W and 140W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the special features for information on Tropical Storm Greg southwest of Manzanillo, Mexico. A surface trough from the coast of southern California southward to off the coast of the Baja California peninsula near 24N120W will continue to block the advance of the subtropical ridge into the region and maintain generally gentle to moderate winds off the Baja California peninsula through late week. Seas will still remain 5 to 7 ft however, in a mix of northerly and longer period south to southwest swell. Farther south, moderate to fresh easterly winds will sweep across the Revillagigedo Islands on the north side of Tropical Storm Greg which is forecast to pass to the south of the region through mid week. Gentle southerly flow will persist across the Gulf of California, except for moderate southerly flow over the northern Gulf. Light to gentle variable winds will prevail across the Gulf of Tehuantepec through midweek before fresh northerly gap winds pulse to strong at night. These winds will likely further increase to fresh to strong by the end of the week into next weekend. 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 seas close to 8 ft. Gentle to moderate southerly winds are expected south of the monsoon trough axis. Long period cross-equatorial southerly swell and 6 to 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 waters later today and raise seas to 6-8 ft through Thu. REMAINDER OF THE AREA... Please see the special features section for information on Hurricane Fernanda. Weak ridging is producing moderate to fresh north to northeast winds north of the 25N. The ridge will build modestly eastward through mid week and tighten the pressure gradient to the north of Fernanda as it moves west of 135W to produce fresh to strong northeast winds across much of the area north of 25N, where seas will build to 8 to 9 ft through midweek in a mix of northerly swell, and southerly swell generated from Fernanda. $$ Christensen