454 AXPZ20 KNHC 282147 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2147 UTC Fri Sep 28 2018 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 2100 UTC. ...SPECIAL FEATURES... Hurricane Rosa centered near 17.7N 117.8W at 28/2100 UTC or 540 nm SW of the southern tip of Baja California moving NW at 5 kt. Estimated minimum central pressure is 955 mb. Scattered moderate to strong convection is observed within 150 nm of the center of Rosa. Swells generated by Rosa will affect the coast of Mexico, including the Baja California peninsula, and southern California during the weekend, and may cause life-threatening surf and rip current conditions. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCPEP5/WTPZ35 KNHC for more details. Farther south, reports from a NOAA P-3 reconnaissance along with data from a recent scatterometer satellite pass indicated winds were already reaching minimal gale force near a 1005 mb low pressure area centered near 11N98W along the monsoon trough, approximately 360 nm southwest of the Gulf of Tehuantepec. A gale warning was already in effect for tomorrow, but given the new data, this was amended to currently valid. Scattered moderate to isolated strong showers and thunderstorms are active within 210 nm of the center of the low pressure. Environmental conditions are conducive for additional development, and a tropical depression or tropical storm is expected to form over the next 48 hours while the low pressure moves west-northwestward well offshore of the coast of Mexico. Seas will build accordingly, possibly reaching 15 ft by Sunday within 120 nm to the north of the low pressure. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A segment of the monsoon trough extends from 08N78W to the low pressure near 11N98W. Another segment reaches form 13N122W to 08N137W. Scattered moderate to isolated strong convection is within 120 nm of the low pressure near 11N98W. Scattered moderate convection is active within 30 nm of the monsoon trough between 122W and 130W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... See Special Features above for information on Hurricane Rosa and the tropical low near 11N97W. A ridge along 27N will retreat ahead of Hurricane Rosa. Gentle to moderate NW flow west of the Baja peninsula will become northerly on Sat, with marine conditions deteriorating across southern waters by Sat night as Rosa approaches the area, with hurricane or tropical storm conditions spreading NE into the waters W of Baja California Norte through early next week. In the Gulf of California, light to gentle southerly winds are expected through Sun night. The southerly flow will increase to near gale force N of 27N thereafter, with tropical storm conditions possible N of 29N Mon night and Tue from Rosa. In the Gulf of Tehuantepec, fresh nocturnal offshore northerly flow will pulse through Sat, becoming strong by Sun night with seas reaching 8 ft by early Mon. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Numerous showers and scattered thunderstorms are likely in the the waters off Guatemala and El Salvador through early Sat. The monsoon trough will meander between 09N and 12N through Tue, with gentle to moderate winds expected on either side of the trough axis. Moderate to fresh E nocturnal drainage flow is expected in the Gulf of Papagayo through Sun night. REMAINDER OF THE AREA... See Special Features above for information on Hurricane Rosa. A broad ridge extends along 27N with gentle anticyclonic flow N of the ridge, and moderate to fresh trades S of 23N. A weak cold front will sweep across the waters north of 27N through early next week, accompanied by a W to NW wind shift. NW swell may propagate into the N central waters early next week. $$ Christensen