Swell Matrix

Area Forecast Discussion

National Weather Service San Diego CA

317 am PDT Sat Oct 21 2017

Synopsis

High pressure aloft and surface high pressure over the Great Basin will bring areas of gusty northeast to east winds, especially below passes and canyons, very low humidity, and hot weather this weekend through Tuesday. The most extreme combination of low humidity, stronger and more widespread winds, and heat is expected on Monday and Tuesday. Winds will weaken Wednesday with cooling spreading inland for Wednesday into next weekend.

Discussion

For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,

High pressure aloft off the Baja coast will expand northward into California and strengthen through Tuesday. Surface high pressure over the Great Basin will bring locally gusty northeast winds near the coastal foothills and below passes and canyons today and Sunday, with more widespread and stronger winds for Monday and Tuesday. This will bring a strong warming trend through Monday. Monday and Tuesday are expected to the hottest days for coastal and valley areas with highs temperatures mostly in the 90s, except 98 to 106 for inland Orange County into the western Inland Empire and for the mesas to the western valleys in San Diego County. The beaches will not be quite as hot with high temperatures mostly in the 80s. Temperatures may not fall below the 70s Monday night in some of the windier coastal foothill locations.

High pressure aloft will begin move westward to a position off the California coast beginning Wednesday with a trough of low pressure developing over the interior western states for the latter half of the week. A cooling trend is expected to develop on Wednesday and extend into Friday and Saturday. The GFS and Canadian models are faster to move this trough of low pressure into the plains on Friday and Saturday with the ECMWF slower and more amplified over the Great Basin and southwest states on Friday before moving it slowly eastward on Saturday. With these scenarios, the cooling would be less with the GFS and greater for the ECMWF.

Aviation

210945z, Coast/Valleys, Areas of low clouds will persist this morning, with bases 2500-4000 ft MSL and tops to 5000 ft MSL. TAF sites could be impacted at times through 18Z, but timing is uncertain. Aft 18Z, mostly clear with unrestricted vis. Gusty northeast winds will develop after 12Z and could impact KSNA, KONT and KSBD through this afternoon.

Mountain/Deserts, Strong and gusty northeast winds develop this afternoon. Winds of 15-30 kt with gusts to 35-45 kt will produce mdt up/downdrafts and LLWS over and west of the mtns.

Marine

Winds and waves continue to subside this morning. Lighter winds and calmer seas are expected through next week.

Beaches

A short-period northwest swell from 290 degrees and a long-period northwest swell from 295 degrees will build through Saturday. This will bring another round of elevated surf from 3-6 ft and an increased rip current threat. Although surf lowers somewhat on Sunday, rip currents will still be a concern. A Beach Hazards Statement is in effect through Sunday afternoon.

Watches, Warnings, Advisories

Ca, Fire Weather Watch from Sunday morning through Tuesday afternoon for Orange County Coastal Areas-Orange County Inland Areas- Riverside County Mountains-Including The San Jacinto Ranger District Of The San Bernardino National Forest-San Diego County Inland Valleys-San Diego County Mountains-Including The Palomar And Descanso Ranger Districts of the Cleveland National Forest.

Red Flag Warning from 10 AM this morning to 6 PM PDT Tuesday for San Bernardino County Mountains-Including The Mountain Top And Front Country Ranger Districts Of The San Bernardino National Forest-San Bernardino and Riverside County Valleys -The Inland Empire-Santa Ana Mountains-Including The Trabuco Ranger District of the Cleveland National Forest.

Excessive Heat Watch from Monday morning through Tuesday evening 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.

Beach Hazards Statement through Sunday evening for Orange County Coastal Areas-San Diego County Coastal Areas.

PZ, Small Craft Advisory until 4 AM PDT early this morning for Coastal Waters from San Mateo Point to the Mexican Border and out to 30 nm-Waters from San Mateo point to the Mexican Border Extending 30 to 60 nm out including San Clemente Island.

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