SLO County weather forecast: More strong winds and rain ahead this week

Happy New Year!

Renowned Central Coast meteorologist Rea Strange told me countless times that when the westerlies (upper-air westerly winds) develop across the Pacific is a sure sign of a prolonged wet pattern for California. The longer-range models show this condition persisting through the first week of January with periods of gale-force southerly winds and moderate to heavy rain.

New Year’s Day will see strong to gale (25 to 38 mph) post-frontal northwesterly winds and clear to partly cloudy skies. Temperatures will remain mild, with the inland valleys (Paso Robles) dropping to the low-40s while the coastal valleys (San Luis Obispo) in the mid-40s. Daytime highs will range between the high-50s and low-60s throughout the Central Coast.

The mid to high-level clouds will increase on Monday morning as a warm front approaches from the west, followed by a cold front on Monday afternoon and night. This system will create strong to gale-force (25 to 38 mph) southerly winds and rain. The rain will end by Tuesday morning. The total rainfall amount from this system should range between 0.50 and 1.25 inches.

A 1,004 millibar storm will develop 1,800 miles west of San Luis Obispo on Tuesday, traveling northeastward and rapidly intensifying to 962 millibars about 600 miles west of Cape Mendocino by Wednesday. Meteorologists refer to this explosive development as bombogenesis, or, “bomb cyclone.” The term describes a rapidly intensifying low-pressure system over a 24-hour time frame. To be classified as a meteorological bomb, a storm needs to lower 24 millibars in 24 hours.

The associated cold front will produce moderate gale-force to fresh gale-force (32 to 46 mph with gusts to 60 mph) southerly winds along the coastline and scattered rain showers on Wednesday. The cold front will pass through the Central Coast on Thursday morning with the strongest winds and heavy rain. The southerly winds will decrease, and the rain will turn to showers on Thursday afternoon and night. Please note this low-pressure system could produce one of the strongest southerly wind events I have seen since the early 1990s. This storm is expected to produce between 2 to 3 inches of rainfall, with much higher amounts in the Santa Lucia Mountains due to orographic enhancement.

Friday will see a break in the weather before another storm creates southerly gales and moderate to heavy rain on Saturday into next Sunday.

Surf report

A series of storms will generate rough oceanographic conditions this week.

A 13- to 15-foot northwesterly (295-degree, deep-water) sea and swell (with a 5- to 12-second period) is expected along our coastline on Sunday.

A 7- to 9-foot west-northwesterly (285-degree, deep-water) swell (with an 8- to 14-second period) will develop along our coastline on Monday, increasing to 9- to 11-feet (with a 14- to 17-second period) on Tuesday.

Increasing southerly winds will generate high southerly seas on Wednesday, followed by a 14- to 16-foot westerly (275-degree, deep-water) swell (with an 8- to 16-second period) on Thursday into Friday, decreasing on Saturday.

A 15- to 17-foot west-northwesterly (285-degree, deep-water) swell (with a 16- to 18-second period) will arrive along our coastline next Sunday.

Seawater temperatures will range between 54 and 57 degrees through Wednesday, warming to 56 to 59 degrees on Thursday into Saturday.

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

John Lindsey is a retired PG&E marine meteorologist. Email him at JohnLindseyLosOsos@gmail.com or follow him on Twitter @PGE_John.