SLO County temperatures about to shoot back up, maybe to triple digits
The autumn equinox, known as the first day of fall, arrives on Sunday at 5:44 a.m. This transition marks the time when the sun will shine directly on the Earth's equator.
The first few days of fall will be warm away from the immediate coastline, with Monday being the warmest day of the week as a ridge of high pressure moves over the Central Coast.
The inland valleys (Paso Robles) will reach the high 90s on Sunday and perhaps triple-digit levels on Monday. The coastal valleys (San Luis Obispo) will warm to the low 80s on Sunday and the high 80s on Monday.
Gentle to moderate (8- to 18-mph) northwesterly winds will allow a persistent marine layer to develop along the beaches with only partial afternoon clearing. This condition will keep the coastal region in the 60s. The marine stratus clouds will continue moving inland overnight with pockets of fog and mist.
A gradual cooling trend is expected on Tuesday and will continue through the end of the week as the ridge of high pressure weakens. The inland valleys will reach the 80s, and the coastal valleys the 70s. The beaches will continue to see overcast skies, with high temperatures ranging from the high 50s to the mid-60s.
The long-range models do not indicate rainfall through the first week of October.
Speaking of the long-range forecast and what this winter may bring: A neutral condition — the infamous "El Nothing" or "El Nada" has been dwelling in Niño 3.4 — a region of sea-surface temperatures in the central equatorial area of the Pacific Ocean — as the standard for classifying El Niño (warmer-than-normal sea-surface temperatures) and La Niña (cooler-than-normal sea-surface temperatures) events.
The fortunetelling sea-surface temperature cycles in Niño 3.4 are categorized by the amount they deviate from the average sea-surface temperature over a three-month period. The Climate Prediction Center is projecting that La Niña is favored to develop into the Northern Hemisphere.
Overall, moderate or strong La Niña conditions typically produce lower-than-average winter rainfall. However, there have been a few La Niña years that have created well-above-average rainfall amounts.
With that said, the predicted La Niña may happen within the context of a larger climate event, a resurgence of a cool phase of the basin-wide Pacific Decadal Oscillation. This event is a long-term fluctuation of the Pacific Ocean that waxes and wanes between cool and warm phases approximately every five to 20 years; it looks like the Pacific is now locked in the oscillation's cool phase.
A multi-year Pacific Decadal Oscillation "cool" trend can intensify La Niña or diminish El Niño impacts around the Pacific basin, according to Bill Patzert, a retired climate scientist at NASA's Propulsion Laboratory in Pasadena.
After reviewing decades of rain data from Cal Poly, we have never seen three years in a row of above-normal precipitation with the cool phase of the Pacific Decadal Oscillation combined with a La Niña condition.
Regrettably, the predicted La Niña, "the diva of drought," coined by Bill Patzert — will probably produce below-average rainfall this season.
At 4 p.m. on Friday, Sept. 27, I will be on the Dave Congalton Show on KVEC Radio for the Guess the First Day of Rain Contest.
Call 805-543-8830 during the show and predict the first day the Central Coast will receive at least 1 inch of rain over 24 hours at any calibrated rain gauge in the region, such as Cal Poly, the Santa Maria or San Luis Obispo airports — or even Rocky Butte.
Surf report
A 3- to 5-foot northwesterly (300-degree deep-water) swell (with an 8- to 12-second period) is forecast along our coastline through Wednesday.
Increasing storm activity in the Gulf of Alaska will produce a 4- to 6-foot northwesterly (290-degree deep-water) swell (with an 8- to 15-second period) along our coastline on Thursday through next Saturday.
Combined with this northwesterly swell will be 2- to 3-foot northwesterly (310-degree shallow-water) seas during the afternoon on Thursday through next Saturday.
A 1- to 2-foot southern hemisphere (225-degree deep-water) swell (with a 15- to 17-second period) is expected to arrive along our coastline on Wednesday through Friday.
Surface seawater temperatures will range between 55 and 57 degrees through Sunday, warming to 57 to 61 degrees on Monday through next Saturday.
On this date in weather history (Sept. 22)
An upper-level low-pressure system southwest of Diablo Canyon produced scattered rain showers and thunderstorms. Over 24 hours, the Ocean Lab Rain Gauge had recorded 0.21 of an inch of rain.
Marine Buoy #42001 — Mid Gulf of Mexico, 180 nautical miles south of Southwest Pass, Louisiana, recorded a pressure drop of -0.70 in/Hg in one hour with significant swell height reaching 38 feet with a 13-second period from Hurricane Rita. For the first time in the historical record, two hurricanes reached Category 5 intensity in the Gulf of Mexico in a single season as Hurricane Rita intensified before making landfall (Katrina and Rita).
San Luis Obispo reached 99 degrees, breaking the previous record of 94 degrees set back in 1983. The high air temperature at the Paso Robles Airport reached 105 degrees.
