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Tropical Storm Hilary Drops Heavy Rain on Southern California

Tropical Storm Hilary dropped heavy rain over parts of southern California on Sunday. At 5:00 p.m. EDT on Sunday the center of Tropical Storm Hilary was located at latitude 31.3°N and longitude 116.1°W which put it about 115 miles (185 km) south-southeast of San Diego, California. Hilary was moving toward the north at 23 m.p.h. (37 km/h). The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h). The minimum surface pressure was 990 mb.

A Tropical Storm Warning was in effect for the portion of the coast from the U.S. border with Mexico to the Point Mugu, California. The Tropical Storm Warning included San Diego. The Tropical Storm Warning also included Catalina Island. A Tropical Storm Warning was in effect for the portion of the coast from Punta Eugenia, Mexico to the border with the U.S. A Tropical Storm Warning was in effect for the portion of the coast from Bahia San Bautista to Guaymas, Mexico.

Former Hurricane Hilary weakened to a tropical storm as the center of Hilary moved over the northern part of Baja California. Bands in the northern part of Hilary’s circulation brought gusty winds to parts of southern California and Arizona. Winds to tropical storm force extended out 230 miles (370 km) from the center of Hilary’s circulation. A weather station at the Imperial, California airport reported a sustained wind speed of 40 m.p.h. (65 km/h) and a wind gust of 61 m.p.h. (98 km/h). A weather station in Yuma, Arizona reported at sustained wind speed of 45 m.p.h. (75 km/h) and a wind gust of 59 m.p.h. (95 km/h).

The circulation around the northern side of Tropical Storm Hilary interacted with an upper level low west of California to drop heavy rain over parts of southern California. Weather stations in Carlsbad, Ramona, Los Angeles, Riverside, Big Bear, Borrego, Palmdale, Edwards Air Force Base, and Gray Butte, California were all reporting heavy rain at 7:00 p.m. EDT.

The upper low west of California will pull Tropical Storm Hilary quickly to the north during the next 24 hours. The center of Hilary’s circulation will pass east of San Diego on Sunday evening. Tropical Storm Hilary continue to weaken as it moves inland over the Southwest U.S. The circulation of Hilary will move over Nevada on Monday. The upper and lower parts of Hilary’s circulation could decouple because of strong vertical wind shear. Tropical Storm Hilary will continue to produce gusty winds and locally heavy rain during the next 24 hours. The heaviest rain is likely to fall where the wind forces the air to rise over mountains. Heavy rain is likely to cause flash floods in some locations. Flood Watches have been issued for parts of southern California, southern Nevada, southern Utah and western Arizona. Hilary could also bring strong winds to mountains in southern Nevada, southern Utah and western Arizona.

Hilary Prompts Hurricane Warning for Baja, Tropical Storm Watch for Southern California

The potential threat from Hurricane Hilary prompted the issuance of a Hurricane Warning for part of Baja California and a Tropical Storm Watch for Southern California on Friday morning. At 11:00 a.m. EDT on Friday the center of Hurricane Hilary was located at latitude 17.9°N and longitude 111.4°W which put it about 360 miles (575 km) south-southwest of Cabo San Lucas, Mexico. Hilary was moving toward the northwest at 10 m.p.h. (16 km/h). The maximum sustained wind speed was 145 m.p.h. (230 km/h) and there were wind gusts to 170 m.p.h. (280 km/h). The minimum surface pressure was 939 mb.

A Hurricane Warning was in effect for the portion of the coast from Punta Abreojos to Punta Eugenia, Mexico. A Hurricane Watch was in effect for the portion of the coast from Punta Eugenia to Ensenada, Mexico. A Tropical Storm Warning was in effect for the portion of the coast from Punta Abreojos to Loreto, Mexico. The Tropical Storm Warning includes Cabo San Lucas. A Tropical Storm Watch was in effect for the portion of the coast from the U.S. border with Mexico to the Orange/Los Angeles County Line. The Tropical Storm Watch included Catalina Island. A Tropical Storm Watch was in effect for the portion of the coast from Ensenada, Mexico to the border with the U.S. A Tropical Storm Watch was in effect for the portion of the coast from Loreto to Huatabampito, Mexico.

Hurricane Hilary continued to intensify on Friday morning. A circular eye with a diameter of 20 miles (30 km) was at the center of Hilary’s circulation. The eye was surrounded by a ring of thunderstorms and the strongest winds were occurring in that ring of storms. Bands of showers and thunderstorms were revolving around the core of Hurricane Hilary. Storms near the core generated upper level divergence that pumped mass away from the hurricane.

The circulation around Hurricane Hilary was large. Winds to hurricane force extended out 45 miles (75 km) from the center of Hilary’s circulation. Winds to tropical storm force extended out 290 miles (465 km) from the center of circulation. The Hurricane Intensity Index (HII) was 29.9. The Hurricane Size Index (HSI) was 16.9 and the Hurricane Wind Intensity Size Index (HWISI) was 46.8. Hurricane Hilary was similar in size and intensity to Hurricane Ida when Ida hit Louisiana in 2021.

Hurricane Hilary will move through an environment favorable for a major hurricane during the next 24 hours. Hilary will move over water where the Sea Surface Temperatures are near 30°C. It will move through a region where the upper level winds are weak and there will be little vertical wind shear. Hurricane Hilary could intensify during the next 24 hours. However, if the inner end of a rainband wraps around the existing eye and eyewall, then concentric eyewalls could form. If concentric eyewalls form, then an eyewall replacement cycle could cause Hilary to weaken.

Hurricane Hilary will move around the western part of a high pressure system over Mexico and the south central U.S. The high pressure system will steer Hilary toward the north-northwest during the next 24 hours. On its anticipated track Hurricane Hilary will move toward Baja California. Hilary will move more toward the north when it reaches the western end of the high pressure system during the weekend. The center of Hurricane Hilary will be near Punta Eugenia on Sunday morning. Hurricane Hilary will start to affect Baja California on Saturday. Hilary will bring strong, gusty winds and locally heavy rain to Baja California. Heavy rain is likely to cause flash floods in some locations.

The center of Hurricane Hilary is likely to approach southern California on Sunday night. There is cooler water west of the northern part of Baja California. Hilary will be weakening when it approaches southern California. Hilary bring strong winds and locally heavy rain to parts of southern California. Heavy rain is likely to cause flash floods in some locations. Flood Watches have been issued for parts of southern California, southern Nevada, southern Utah and western Arizona.