25/211 AM.
High temperatures will remain above normal through Saturday with areas of low clouds and fog each morning. Substantial cooling is expected Sunday and Monday. Beach impacts from Tropical Cyclone Polo are possible Monday and Tuesday in the form of high surf and possible beach erosion. A significant warming trend is expected Tuesday and Wednesday.
(tdy-Sun), 25/1001 AM.
***UPDATE***
Overall not much change in weather conditions today vs yesterday. There is still about a 1mb onshore trend today, though the marine layer depth lowered slightly to around 1600 feet in the LA Basin and around 1000 feet along the Central Coast. Expecting highs today be within 1-3 degrees of yesterday in most areas except the mountains where temps will be 3-6 degrees cooler.
For Saturday expecting at least a few degrees of warming across the LA/Ventura coast and valley areas due to a 1-2mb offshore trend and a little bit of northeast flow aloft. Highs in Downtown LA have around a 50-60% chance of reaching 90 and similar chance for the warmer valleys to reach 100. However, elsewhere highs Saturday will cool between 2 and 5 degrees from today.
***From Previous Discussion***
Marine layer clouds this morning overspread the Central Coast and are starting to spread into the inland coasts south of Point Conception. Expecting these clouds to burn off by mid to late morning. Daily highs are expected to be a few degrees above normal through Saturday, then lowering Sunday and Monday before additional warming starts again next Tuesday. For the next two days, highs will be around 4 to 6 degrees above normal, and 8 to 10 degrees above normal in the warmest areas. Sunday and Monday most areas away from the coast will be a few degrees below normal. However, closer to the coast the high sea surface temperatures will keep coastal sections slightly above normal, in the 70s to near 80.
Winds are currently fairly weak across the area, except for gusty onshore winds through some passes and canyons of LA County, strongest into the Antelope Valley. Onshore gradients are forecast to gradually increase through the next couple of days, so expect these onshore winds (currently gusting to 35 mph at Lake Palmdale) to increase some during this time. In addition, the Santa Barbara to Santa Maria gradient will strengthen with potential for some gusty Sundowner winds over SW Santa Barbara County Saturday night or more likely Sunday night.
(Mon-Thu), 25/210 AM.
Still plenty of uncertainty next week as Polo and Odalys swirl off central Mexico. In an odd twist, the two storms are actually slowly moving towards each other and this will present some tricky track issues that may not be resolved until late this weekend. In the meantime, most of the ensemble solutions move Polo northwest, then inland over central Baja, while Odalys will soon shift to a slow move to the north. There is relatively high confidence that southern California will be impacted by southerly swells early next week. However, much less confidence in any rain chances, especially with the latest forecast tracks favoring a landfall for Polo somewhere in Baja Sur. Guidance seemed undecided in how much PWAT values will increase Sunday into Monday, so will have to wait to see if PWATs or other precip related parameters come into better alignment over the next few days. Aside from that, some of the ensemble solutions have been indicating an increase in offshore flow Tuesday and Wednesday leading to 10-15 degrees of warming. However, still relatively low confidence in that pending where the tropical systems track.
25/1628z.
At 16Z over KLAX, the marine layer was 1400 ft deep. The top of the inversion was at 3000 feet with a temperature of 24 Celsius.
High confidence in VFR conditions through at least Saturday for KPRB, KPMD, and KWJF.
High confidence in clearing at all sites by 19Z today.
For tonight into tomorrow: LIFR/IFR conditions possible at KSBP (20%) and KSMX (60%). IFR/MVFR conditions possible at KOXR (30%), KCMA (30%), KSMO (50%), KLAX (70%), KLGB (70%), KBUR (30%), KVNY (20%). Moderate confidence in timing (plus or minus 3 hours).
High confidence in typical winds.
KLAX, VFR conditions likely to start 17-18Z. There is a 20% chance of brief MVFR ceilings 23-03Z. There is a 70% chance of OVC008-012 tonight, low-moderate confidence on timing. High confidence in any east winds staying under 8 knots.
KBUR, MVFR HZ possible through 20Z, otherwise high confidence in VFR conditions through at least 10Z. There is a 30% chance of IFR ceilings 12-16Z on Saturday.
25/934 AM.
Through this weekend, moderate confidence Small Craft Advisory (SCA) winds and steep seas affecting the outer waters of the Central Coast. Winds will be strongest this evening, when the nearshore waters will see brief SCA conditions.
High confidence in widespread gusty winds Monday into Tuesday over most of the coastal waters, including nearshore. SCA likely everywhere, with a moderate risk for Gales between Point Sal and San Nicolas Island.
Southerly swells from Hurricanes Odalys and Polo will affect the region this weekend through the middle of next week. These swells will create larger waves nearshore, which could impact some harbor entrances, especially Sunday through Tuesday.
Some dense fog is possible on the Central Coast this weekend.
25/949 AM.
Southerly swells from Hurricanes Odalys and Polo will affect the region this weekend through the middle of next week. This is a very complicated scenario with two hurricanes so close in proximity, with one of them (Odalys) poorly handled by our computer models. Another complexity is the relatively short window of time that Polo is far enough to the west for its waves to have a clear path towards southern California. This means that the swells will have a sharp peak and narrow window of time to line up with the high tides. Lastly, some south-facing shores are extra vulnerable because of the lingering erosion effects of Hurricane Marie from earlier this month.
While the surf heights will likely range in the 4 to 7 foot range for south facing beaches at times Sunday through Tuesday, there is a plus or minus in that potential of 2 feet or so due to the complications mentioned above. High tides will steadily build each day and peak Monday and Tuesday, likely reaching around 7 feet (MLLW) - which is higher by almost a foot over astronomical tides due to ongoing effects of El Nino.
There is a significant concern for Coastal Flooding over vulnerable south-facing beaches as a result, but the magnitude is still uncertain. The areas of most concern include Avalon, Long Beach, Malibu and Santa Barbara. The reasonable worst-case scenario is for impacts similar the Hurricane Marie from earlier this month, but the most likely outcome is for impacts to be a step less. The one exception being Avalon on Catalina Island, as the swells from Hurricane Polo will be more from a southeasterly direction than with Marie, which they are more exposed to. The same goes for Santa Barbara Harbor, but being the furthest away from the Hurricane, the risk is less but still present.
South-facing beaches should plan for shallow flooding of seawater over low lying beach walkways, parking lots, and roads as well as significant beach erosion. Very localized damage to structures is possible in the most vulnerable areas. With all that stated, there is a potential that impacts are minimal if the lower-end surf outcome materializes.
A decision will be made later today on if a Beach Hazards Statement or Coastal Flood Advisory will be issued.
Ca, NONE. PZ, Small Craft Advisory in effect from 3 PM this afternoon to 9 PM PDT this evening for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 9 AM PDT Saturday for zones 670-673. (See LAXMWWLOX).
