000 AXPZ20 KNHC 261642 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Wed Jun 26 2019 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 1500 UTC. ...SPECIAL FEATURES... Newly upgraded Tropical Storm Alvin is centered near 14.7N 109.4W at 1500 UTC, or about 490 nm, or 915 km, from the southern tip of Baja California, moving W at 12 kt. Estimated minimum central pressure is 1005 mb. Maximum sustained wind speed is 35 kt with gusts to 45 kt. Satellite analysis suggests that Alvin is a small system with tropical storm force winds extending only 30 nm from center across the NE quadrant. Scattered moderate to strong convection has increased around the center this morning and is occurring within 90 nm across the east and 75 nm across the western semicircles. Alvin is expected to continue on a westward motion for the next 24 hours and strengthen modestly, then begin to veer more WNW through Fri and slowly weaken as it encounters drier more stable air. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP1/WTPZ21 KNHC for more details. Strong gap winds are expected across the Gulf of Tehuantepec starting Thursday morning, and are forecast to strengthen to minimal gale force early through late Friday morning. Strong winds will continue through the weekend, and may pulse again to minimal gale force again Saturday morning. Peak seas will build to 12 ft or higher downstream of the Gulf Friday morning and begin to merge with easterly wind swell propagating away from a strong gap wind event across the Gulf of Papagayo region during this same time period. ...TROPICAL WAVES... A tropical wave is analyzed along 87W-88W from Nicaragua to 01N, moving W around 15 kt. Scattered moderate to strong convection is located near the monsoon trough near the wave, and well west of the wave axis across the Gulf of Tehuantepec north of 12N. A tropical wave is along 126W from 02N to 15N, moving westward around 15 kt. Dry stable air to the north of this wave is pushing southward to near the ITCZ in this area, and limiting convection near the wave. Widely scattered moderate convection is seen along and within 120 nm south of the ITCZ, between the wave and 120W. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 0N74.5W TO 09.5N86W TO 10N104W. The ITCZ is from 09.5N115W TO 10N134W to beyond 08.5N140W. Scattered moderate to strong convection is noted within 150 nm of the trough between 83W and 102W, and from 12N to 15N between 92W and 98W. Scattered strong convection is from 06N to 10.5N between 135W and 140W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... See the Special Features section above for details regarding newly upgraded Tropical Storm Alvin, the first tropical cyclone of the Northeast Pacific Hurricane season. A broad and weak ridge extends southeastward from a 1024 mb high center near 34N141W, to just SW of the Revillagigedo Islands. The pressure gradient on the east side of this ridge is supporting gentle to moderate NW winds across the offshore waters of Baja California. Altimeter data this morning shows wave heights ranging around 4 ft to 5 ft well offshore, and 3 ft near the coast. Tropical Storm Alvin will continue to move westward and away from Mexico during the next few days and allow the ridge to adjust and build very modestly into the offshore waters. This will maintain a moderate NW wind flow and mainly 4- 5 ft seas across the waters through Fri. Look for strong afternoon winds late Fri across Baja California Norte to the Punta Eugenia area, with seas building to near 6 ft. As Alvin moves farther away from the central Mexican coastline, winds and seas will diminish moderately, becoming E at 10-15 kt with seas around 5 ft by Thu. The next tropical wave approaching the Gulf of Tehuantepec will induce active weather across the offshore waters, and fresh offshore winds ahead of it Thu. A strong gap wind event is expected for Tehuantepec Thu night into Fri, and gale force winds are expected. Winds between Cabo Corrientes and Puerto Angel will shift NW to N by Fri as the ridge builds into the area behind the exiting Alvin. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Moderate to fresh offshore gap winds prevail across most of the Central American offshore waters this morning, between Papagayo and 90W, and are expected to increase in the next few days as high pressure resides due north of the area across the Gulf of Mexico. Strong gap winds are forecast to develop across the Papagayo region late tonight through Thu and extend will downstream to 92W or beyond. This large area of strong NE to E winds will build seas to 8-9 ft and extend beyond 90W and will eventually mix with northerly wind waves propagating away from Tehuantepec late Fri through the weekend. Nocturnal winds are expected to pulse to 30 kt across Papagayo early Fri morning, with downstream seas building 8-10 ft. Elsewhere moderate S to SW winds will prevail south of the monsoon trough, with cross equatorial SW swell maintaining seas at 4-6 ft for the next few days. REMAINDER OF THE AREA... The broad ridge across the area waters is producing moderate to locally fresh trade winds to the south of the ridge, mainly from 10N to 18N and west of 120W. Seas across the tradewind belt are running 6-8 ft in mixed swell and tradewind waves. Little change in the position of the high or the strength of the trades is expected for several days. Wave heights in this area will generally run 6-7 ft. The weakening remnants of Alvin are forecast to cross 120W late Fri through Sat and will still be accompanied by a moderate sized wave field with seas to near 8 ft. Farther south, long-period cross-equatorial swell is maintaining wave heights around 8 ft south of 032N and west of 105W. As the swell energy continues to decay, the area of 8 ft seas will gradually shrink in coverage to south of the equator through Thu. New southern hemispheric SW swell will move into the regional waters over the weekend and cause seas south of 05N between 105W and 125W to build to between 7 and 9 ft by Sun evening. $$ Stripling