26/758 PM.
Substantial cooling is expected across the area Sunday and Monday. Beach impacts from Tropical Cyclones well south of the region are expected to peak Monday and Tuesday in the form of high surf, beach erosion, and possible coastal flooding. A significant warming trend is expected Tuesday and Wednesday.
(Sat-Tue), 26/733 PM.
***UPDATE***
High clouds are have reached southern California, which will likely disrupt marine cloud formation, especially south of Point Conception. Lower confidence on marine layer clouds and patchy fog for the coasts, but somewhat higher confidence in clouds for the Central Coast. Despite the high clouds, we could still see some brief marine layer clouds and patchy fog form during the early morning hours for coastal Ventura County and southward.
Guidance appears to be trending toward a drier solution for Sunday and Monday, as this upper level low passing through appears to be moisture starved. Any showers (10-15% chance) that form should carry little to no impacts. However, additional clouds and colder temperatures will translate to 5 to 10 degrees of cooling Sunday/Monday. Weak northerly offshore winds start to develop early Monday, with some borderline advisory level Sundowner winds by Monday evening. Offshore gradients peak around 3.0 mb Tuesday morning, and still appear to favor a fairly northerly direction. This supports a 6 to 15 degree boost in Tuesday's high temperatures.
***From Previous Discussion***
An upper level trough is expected to dig southward over the area Sunday into Tuesday. This feature will steer Hurricane Polo into Baja California Sur and keep most of the moisture south and east of our CWA. There is still a handful of ECWMF ensemble guidance that brings enough moisture to produce some light showers over LA county, so have left 15% POPs in despite the downward trend. This trend is due to a better handling of the trough and its timing. There also could be a few light showers across the far interior solely due to trough dynamics, but most likely will just remain dry. Onshore pressure gradients will respond to the height falls with NAM/ECWMF values around +4mb. This will result in gustier winds across the interior strongest over LA county. Not expecting any advisories but wouldn't be surprised to see some local gusts to 45 mph Sunday afternoon/eve over eastern San Gabriels. There is a moderate chance for low-end advisory Sundowners on Monday.
The biggest concern in the short-term is the southerly swells produced by Hurricane Odalys and Polo. Especially considering that the LA/VTA coastline has enhanced vulnerability due to Hurricane Marie over Labor Day. Most hazardous conditions are expected Monday and Tuesday when high tides overlap with the continuing southerly swells. Please read the beaches/marine sections of the AFD for more information. For even more details, refer to CFWLOX.
With the cooling trend, temperatures should be a bit below normal by Monday (especially across far interior). Near normal close to the coast. Trough will exit east with ridging building in from the west which will result in a flip into offshore flow and warming temperatures.
(Wed-Sat), 26/100 PM.
Guidance is generally in agreement mid next week for building ridging over the area and likely some offshore flow. There is quite the uncertainty in the evolution of the ridge & exactly how much offshore flow will occur. Although decent confidence that is will be warm with about a 30-40 percent chance of near 100 degree temperatures in the valleys and similar chances for Downtown LA and San Luis Obispo reaching 90 or higher.
National Hurricane Center is tracking a developing disturbance south of the Gulf of Tehuantepec. Current projections indicate that this system will likely strenghten significantly. If this does occur, the upper-level ridging would steer this system west- northwest for quite some time putting it in a favorable position for southerly swell impacts for the beaches. We will have to keep an eye on this system because there is a chance it produces a building southerly swell which could result in impacts at the beaches. However, this is rather far out and would not see impacts until probably after October 4th.
27/0124z.
At 2154Z at KLAX, there was no marine layer. There was a surface based inversion with a top at 1500 feet with a temperature of 27 Celsius.
High confidence in VFR TAFs for KPRB, KBUR, KVNY, KWJF, and KPMD.
Low confidence in flight cats tonight for remaining TAFs. Chance for no low clouds tonight at KSBP (50%) and KSMX (30%). There is a 20-40% chance for IFR-MVFR cigs tonight at remaining sites, highest for KLAX/KLGB/KSMO, highest chances from 13-15Z. South of Point Conception cigs would likely be patchy and may frequently bounce between SCT and BKN if they form.
KLAX, High confidence in TAF through 06Z, then low confidence in flight cat thereafter. 40% chance for BKN007-012 conds 10Z-17Z. If cigs form they may bounce between BKN and SCT frequently.
Moderate to high confidence in TAF through 18Z Sat and after 03Z Sun, otherwise high confidence. CIGs may scatter and reform several times due to high level clouds this morning. There is a 30% chance of BKN008-012 CIGs after 03Z Sun. High confidence in no significant east win component.
KBUR, High confidence in VFR TAF.
26/817 PM.
Through this weekend, high confidence in Small Craft Advisory (SCA) winds and steep seas affecting the outer waters. The current SCAs have been extended through Tuesday night. Gale force gusts will be possible at times, especially Monday afternoon and evening across the far southern waters (PZZ676). Nearshore along the Central coast will see SCA winds and steep seas again Sunday and Monday in the afternoon and evening, and likely again on Tuesday.
For the nearshore waters south of Point Conception, there will be a chance of SCA winds over the western Santa Barbara Channel Sunday and especially Monday during the afternoon and evening, and likely again on Tuesday.
Southerly swells from Hurricanes Odalys (SSW) and Polo (SSE) will affect the region this weekend through Tuesday. These swells will create larger waves and surf nearshore, which could impact some harbor entrances, especially Sunday through Tuesday. For the waters off the LA Coast, SCA winds are likely Monday afternoon and evening over the western portion.
26/823 PM.
Southerly swells from Tropical Cyclones Odalys and Polo will affect the waters through the middle of next week, with Hurricane Polo likely sending the more impactful swell from the SSE, affecting our coastline Monday and Tuesday. This swell timing will line up with very high tides Monday and Tuesday in the late morning hours. Lastly, some south-facing shores are more vulnerable because of the lingering erosion effects from Hurricane Marie earlier this month.
Surf heights across Los Angeles and Ventura Counties are likely to peak around 4-7 foot Monday and Tuesday, while the Santa Barbara south coast should see surf in the 3-5 foot range. High tides will steadily build each day and peak Monday and Tuesday, likely reaching around 7 feet (MLLW) in the late morning hours - which is higher by almost a foot over astronomical tides due to ongoing effects of El Nino.
While this swell is slightly smaller than the swell from Marie, there is a significant concern of Coastal Flooding over vulnerable south-facing beaches. The areas of most concern include Avalon, Long Beach, Malibu and Santa Barbara. The reasonable worst-case scenario is for impacts similar to those from Hurricane Marie, 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 where 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 potential for significant beach erosion. Very localized damage to structures is also possible in the most vulnerable areas.
Beach Hazards Statements are in effect for LA, Ventura, and the Santa Barbara south coast. Then a Coastal Flood Advisory and High Surf Advisory are in effect for LA and Ventura Monday and Tuesday.
Ca, Beach Hazards Statement in effect through late Sunday night for zones 87-354-362-366. (See LAXCFWLOX). Coastal Flood Advisory in effect from 5 AM Monday to 5 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). High Surf Advisory in effect from 5 AM Monday to 5 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect through Wednesday afternoon for zones 349-350. (See LAXCFWLOX). PZ, Small Craft Advisory in effect from 3 PM Sunday to 3 AM PDT Monday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Tuesday for zones 670-673-676. (See LAXMWWLOX).
