08/801 PM.
Temperatures across the region are expected to trend cooler Friday into Sunday and there will be an increasing chance of showers and thunderstorms due to moisture from Hurricane Rachel. These showers could persist into Tuesday, with another warming trend possible Wednesday through Friday.
(Thu-Sun), 08/918 PM.
***UPDATE***
A final day of extreme heat ended with highs in the mid 90s to 102 degrees away from the coast, with coastal highs in the upper 70s to mid 80s. An upper ridge over the region will weaken as an upper low west of Monterey moves SSE and heights lower across the area. In addition, surface pressure gradients are now onshore and will continue to strengthen over the next couple of days. The end result will be much cooler weather Friday through early next week. The highs Friday will be in the mid 70s for the coasts, except 60s for the Central Coast, with 80s to mid 90s further inland. With the lowering heights and return to onshore flow, the marine layer will likely shift farther inland, covering more of the coastal basins and extending into some of the coastal valleys.
Additional cooling along with increasing low clouds and fog in the morning will be accompanied by mid to upper level clouds moving over the area. The upper low off the coast will continue to move southward heading toward TS Rachel, as a longwave trough forms along the West Coast. By Saturday evening, these systems are forecast to merge and move inland across the SoCal/Baja border. This will produce a chance of showers fueled by tropical moisture Saturday evening through early Tuesday, mainly south of Point Conception, although with light rain possible further north. While some uncertainty remains as to rain amounts, the totals over Ventura and LA Counties will generally be between 0.25 to 0.50 inches but up to 1.0 inch in the mountains. Farther north, amounts will likely be 0.10 inch or less.
By Sunday, temperatures will be in the 70s in most places, but with a significant increase in moisture it is likely to feel very muggy. A very low but non-zero chance of thunderstorms will accompany these showers.
***From Previous Discussion***
The main forecast issue moving forward is the uncertainty with the the track of Rachel and the potential impacts. Swells have already started to arrive on our southern beaches and impacts will increase through Sunday. The last few tracks of Rachel have trended farther south but most of the ensemble solutions indicate at least some tropical showers south of Pt Conception by Sunday, and around 10% of the solutions show over an inch of rain.
Later Sunday into Monday an upper low will move south into southern California and possibly interact with lingering tropical moisture to generate additional shower into Monday.
(Mon-Thu), 08/1213 PM.
On Monday the upper low will move into the vcnty of SBA county with 557 dam hgts. The low will bring clouds and chc of rain to the entire 4 county forecast area from midnight to midnight. Since most of the moisture will be to the east of the area rainfall totals will not be that great most areas can expect to recieve a tenth to a quarter inch of rainfall. Max temps will fall further to the mid 60s to lower 70s.
There is some disagreement on how fast the upper low will move out of the area. Enough solutions keep the upper low around long enough to keep a 20 to 30 percent chc of rain in the forecast. Even if it does rain there will not be much additional rainfall.
Aside from a small chc of a mtn shower Wednesday should be dry as drier NW flow moves into and over the state. Sunnier skies and rising temps will bring 3 to 6 degrees of warming. Even with the warming max temps will end up about 6 degrees blo normal.
09/0410z.
At 0400Z at KLAX, the marine layer was 800 feet deep. The top of the inversion was 3500 feet with a temperature of 27 degrees Celsius.
For 06Z TAF package, high confidence in KPRB, KBUR, KVNY, KPMD and KWJF as CAVU conditions are expected through the period.
For coastal sites, moderate confidence in 06Z TAFs as timing of flight category changes could be +/- 3 hours of current forecasts and possibly off by one flight category.
KLAX, Moderate confidence in 06Z TAF. Timing of flight category changes could be +/- 3 hours of current forecasts. There is a 30-4% chance of LIFR conditions 08Z-14Z. No significant easterly wind component is expected.
KBUR, High confidence in 06Z TAF as CAVU conditions are expected through the period.
08/747 PM.
Relatively quiet conditions are expected across the coastal waters through much of Saturday. Localized Small Craft Advisory (SCA) gusts may occur each afternoon and evening between Point Conception and San Nicolas Island. Night through morning dense fog may affect portions of the coastal waters adjacent to the Central Coast and south to San Nicolas Island once through Friday morning (Oct 9th).
Northwest to southwest winds will increase to 20-30 knots by Saturday afternoon/evening, becoming much more expansive all of Sunday and into early Monday morning. There is a 30-40% chance of Gale Force winds on Sunday, primarily focused across the nearshore waters adjacent to Los Angeles and Orange Counties. Large, steep, and choppy seas will develop Saturday, continuing through at least Monday. This fairly rapid and significant increase in winds is due to a very complex situation as an unseasonably cold trough drops down the California Coast, interacting with remnants of Tropical Storm Rachel, which will soon turn northeast and move towards the California/Mexico Border coastline over the next couple of days. It is worth noting that the projected track of Tropical Storm Rachel has shifted further south, most likely making landfall in northern Baja California.
In addition the the increasing gusty winds, widespread light to moderate rainfall is likely Saturday evening through Tuesday, with highest confidence for Sunday-Monday. There is a 10% chance of thunderstorms during the same timeframe. While showers or thunderstorms are possible anywhere, highest chances exist south of Point Conception.
As this is a complex and evolving situation, please continue to monitor the forecast.
08/747 PM.
A Coastal Flood Advisory is in effect through Tuesday afternoon for Los Angeles and Ventura Counties, while a Beach Hazards Statement (BHS) is in effect for the Santa Barbara South Coast and the Central Coast.
A very complex series of swells from the south, west, and northwest will impact our coastlines into at least early next week. Energy from Tropical Storm Rachel, southern hemisphere swells, northwest swells, and local wind swells will add up with each other to produce elevated surf and dangerous rip currents at times. Extremely high tides will be common each morning, peaking between 6.8 to 7.6 feet MLLW, highest further south. Additionally secondary high tides will peak each evening, likely most impactful through the weekend with tides reaching 5.5 to 6.5 feet MLLW.
While each day under the Coastal Flood Advisories or BHS should see fairly similar impacts, Sunday will likely see elevated impacts. Rapidly increasing wind speeds will likely add to the coastal flooding potential, creating a wind swell as well as elevating tides slightly. Additionally, if Rachel's track deviates a bit more to the north that would result in lower mean sea level pressure contributing to even higher water levels. If all these ingredients overlap on Sunday, a more significant coastal flooding event will be likely. This is a very narrow window, but there is a low chance for a targeted Coastal Flood Warning to be issued in southern Los Angeles County if all factors line up.
As this is a complex and evolving situation, please continue to monitor the forecast.
Ca, Coastal Flood Advisory in effect until 2 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect from Saturday morning through Monday afternoon for zones 340-346-349-350. (See LAXCFWLOX). PZ, NONE.
