441 AXPZ20 KNHC 281609 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1609 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 1200 UTC surface analysis and satellite imagery through 1500 UTC. ...SPECIAL FEATURES... Hurricane Rosa centered near 17.2N 117.5W at 28/1500 UTC or 550 nm SW of the southern tip of Baja California moving NW at 6 kt. Estimated minimum central pressure is 942 mb. Maximum sustained wind speed is 120 kt with gusts to 145 kt. Scattered moderate to isolated strong convection is observed within 120 nm of the center of Rosa. Swells generated by Rosa will affect western 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. Showers and thunderstorms are increasing within 90 nm of a 1005 mb area of low pressure near 11N97W. While this low is currently poorly organized, the low pressure will drift WNW and gradually become better organized through tonight. Environmental conditions are conducive for development, possibly into tropical cyclone this weekend. A gale warning is in effect for the waters beyond 120 nm off the coast of Guerrero and Michoacan starting late Sat. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A segement of the monsoon trough extends from 08N78W to low pressure near 11N97W to 15N107W. Another segment reaches form 13N124W to 09N136W. The intertropical convergence zone continues west from 09N136W to beyond 140W. Scattered moderate convection is within 90 nm off the low pressure near 11N97W. ...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, nocturnal offshore northerly flow will pulse to fresh the next several days with seas building to 7 ft during strongest winds. 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 series of weak cold fronts or troughs will sweep across the far NW waters through the weekend, accompanied by a W to NW wind shift. NW swell may propagate into the N central waters early next week. $$ Christensen