This long-duration heatwave will continue for the coast and valleys through Thursday and through Friday for the lower deserts. Cooling will spread inland for Friday and Saturday, but will remain above normal. For Sunday through early next week, a low pressure system along the West Coast and off the coast of Baja may draw moisture from what was Hurricane Rachel northeastward and into the area with a chance of showers.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION,
(today through Friday),
Today marks day five of the current heatwave. Widespread Major to Extreme HeatRisk will continue through Wednesday for the coasts and valleys, as heat stress compounds over time especially given the warm overnight lows. Today several calender day high records may be broken (updates on this may be available later this evening). A small increase in the afternoon sea breeze has resulted in temperatures a few degrees cooler near to the coast compared to yesterday. Gradual cooling is anticipated each day through Friday for coasts and valleys, and HeatRisk will drop to mostly Moderate to Major for those areas. Expect highs around 12 to 18 degrees above average for the coast and valleys. Across the low deserts temperatures will increase by a few degrees tomorrow with highs of 104 to 108 widespread with Major HeatRisk, which is around 10 to 15 degrees above normal. The Extreme Heat Watch for the deserts has been upgraded to an Extreme Heat Warning in effect from 10 AM Wednesday through 8 PM Friday. At this point, Heat Warnings will probably be allowed to expire Thursday evening for areas other than the low deserts on Friday, but Heat Advisories are very possible for Friday.
Surface pressure gradients and thus onshore winds will increase slightly each day, and by Wednesday or Thursday a shallow marine layer is likely return, starting with clouds and possibly dense fog along the coasts. The marine layer will slowly deepen into the weekend with increased coverage of clouds.
(Saturday through Tuesday), Cooling trends will continue into this weekend with as a fairly deep trough will likely build down the West Coast. Limited to no heat impacts are expected for the first time in awhile by this Sunday with highs generally in the 70s and 80s, hottest towards the interior.
The National Hurricane Center shows the remnant low from what was Hurricane Rachel approaching the northern Baja of California this weekend and will likely pass through this region by early next week. If the storm tracks closer to the region (40-50 percent chance), generally light showers within a tropical airmass are possible Sunday and Monday in particular, focused south and east of Orange County and across the mountains.
Gusty onshore winds may approach advisory levels for favored passes mountains and deserts Sunday or Monday.
062240z, SCT shallow cumulus clouds based near 10 kft over the mountain ridges dissipating by 03Z. There is a 40% chance of CIGS below 500 ft and fog with vis 1 SM or less developing along the coast 09-18Z, though chances of these low CIGs/VIS at the coastal TAF sites are less than 30%. Higher chances of low clouds and fog returning to the coastal areas Wed night.
No hazardous marine conditions are expected through Saturday.
Increasing south swells will create surf of 3-5 feet with sets to 6 feet on south and southwest facing beaches Wednesday through Friday. Strong rip and longshore currents are expected. In addition, this elevated surf will combine with high tides during the mornings and evenings to generate local coastal flooding and beach erosion. The Beach Hazards Statement and Coastal Flood Advisory contain the details.
Ca, Extreme Heat Warning until 8 PM PDT Thursday for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas-San Diego County Valleys-Santa Ana Mountains and Foothills.
Beach Hazards Statement through Friday evening for Orange County Coastal Areas-San Diego County Coastal Areas.
Coastal Flood Advisory from 6 AM Wednesday to 11 AM PDT Friday for Orange County Coastal Areas-San Diego County Coastal Areas.
Extreme Heat Warning from 10 AM Wednesday to 8 PM PDT Friday for Coachella Valley-San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
