000 AXPZ20 KNHC 201615 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Sun Aug 20 2023 Tropical Weather Discussion for the eastern Pacific Ocean from 03.4S to 30N, east of 120W including the Gulf of California, and from the Equator to 30N, between 120W and 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 downgraded Tropical Storm Hilary is centered near 29.7N 115.9W at 1500 UTC, moving north-northwest at 22 kt. Estimated minimum central pressure is 984 mb. Maximum sustained wind speed is 60 kt with gusts to 75 kt. Seas to 12 ft or greater are found within 120 nm NE, 420 nm SE, 360 nm SW, and 180 nm NW quadrants, with peak seas to 24 ft across the Baja offshore waters and estimated to 18 ft inside the Gulf of California. Scattered moderate convection is occurring north of 29.5N and east of 117.5W. Scattered moderate isolated strong convection is elsewhere across the Gulf of California north of 27N and east of 113W. Scattered strong convection has recently developed along the western slopes of the mountainous terrain of northern Sinaloa and southern Sonora. Continued weakening is expected today as Hilary races northward. Hilary will move along and into the coast of Baja California Norte during the next several hours and across Southern California this afternoon. Preparations for flooding impacts associated with Hilary should be completed as soon as possible, as heavy rainfall has begun. In the Southwestern United States, the potentially historic amount of rainfall is expected to cause flash, urban, and arroyo flooding including landslides, mudslides, and debris flows. Dangerous to locally catastrophic flooding impacts are expected through Monday morning. Large swells generated by Hilary will affect portions of the Baja California Peninsula, southern California, and coastal areas inside the Gulf of California through early Tue. This swell will produce enormous-sized surf and life-threatening rip current conditions. Please consult products from your local weather office. Please read the latest HIGH SEAS FORECAST issued by the National Hurricane Center at website https://www.nhc.noaa.gov/text/MIAHSFEP2.shtml and the latest Hilary NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. ...TROPICAL WAVES... An Atlantic tropical wave along 86W-87W extends southward across Honduras and Nicaragua to the Pacific waters N of 08N. Scattered to numerous convection is described below. A tropical wave is along 104W, north of 03N and moving westward at 10-15 kt. Scattered convection is described below. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 10N74W to 06.5N82W to 10N105W, then resumes from 12.5N119W to 08.5N133W to 09N140W. Scattered to numerous moderate to strong convection is noted from 02N to 09N E of 90W. Scattered moderate to strong convection is noted from 05N to 14N between 90W and 105W, from 10N to 16N between 111W and 120W, and from 05.5N to 09.5N west of 127W. ...OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the Special Features section for information on Hurricane Hilary. Strong convection has begun to develop in the past few hours near the coasts and along the western slopes of the mountains of Sinaloa and southern Sonora, and will likely increase in the short term. Strong southerly winds persist across the southern Gulf of California, where seas are estimated at 7 to 12 ft. Outside of the influence of Hurricane Hilary, isolated showers and thunderstorms are noted in the Mexican offshore waters, but become scattered to the south of 17N across the outer waters offshore of Cabo Corrientes. Farther southeast, moderate NW to N winds generally prevail, with seas 6-8 ft in NW swell. A narrow plume of strong northerly gap winds continues this morning across the central Gulf of Tehuantepec, where seas are 4-7 ft. For the forecast, winds and seas associated with Hilary will diminish over Mexican offshore waters today through early Mon as the storm quickly moves north of the area. Strong to near gale force gap winds will pulse across the Gulf of Tehuantepec through Thursday, strongest at night. Looking ahead, another area of low pressure has a low chance of development off southern Mexico through the middle of the week. ...OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Overnight satellite-derived wind data depicted fresh NE-E gap winds in the Papagayo region. Seas in these waters are 5-6 ft. Moderate or weaker winds and seas of 3-5 ft are prevalent in the rest of the area N of 08N. To the south of 08N moderate to locally fresh W to SW monsoon winds prevail, where seas are 5-7 ft in S and SW swell. For the forecast, moderate to fresh E winds will pulse at night across the Gulf of Papagayo region through Tue. SW monsoonal winds will increase S of 09N beginning today between Colombia and waters north of the Galapagos, then increase offshore of Costa Rica and western Panama Mon and Tue. Winds will then diminish late in the week as the monsoon trough lifts northward. Seas will build to 10 ft in the area described. ...REMAINDER OF THE AREA... Overnight scatterometer satellite data showed fresh to strong southerly winds from 08N to 16N and between 109W and 123W. These winds are associated with strong convection in the area where low-level converges in the southerly flow feeding into the south side of Hilary. Seas in these waters are 8-10 ft. Elsewhere in the basin, a weak pressure pattern prevails W of Hilary, sustaining moderate or weaker anticyclonic winds and moderate seas of 6-9 ft in SE swell from Hilary. For the forecast, SW winds will start to increase south of the monsoon trough and east of 110W today and continue through midweek with building seas. $$ Stripling