29/227 AM.
Beach impacts from Tropical Cyclones well south of the region are expected today in the form of high surf, beach erosion, and possible coastal flooding. A major heat wave will begin to develop today and will peak Friday and over the weekend with dangerously hot temperatures and periods of weak Santa Ana winds.
(tdy-Thu), 29/939 AM.
***UPDATE***
Temperatures will be warming today as a light offshore flow has developed which in turn will delay the arrival of the sea breeze. Not really expecting much in the way of offshore winds except for some gusty north winds in the mountains, mainly Santa Barbara County. High temperatures are expected to be 5-10 degrees warmer than yesterday and locally as much as 15 degrees warmer. The good news though is humidities are way down, as much as 60% lower than yesterday due to the offshore flow.
***From Previous Discussion***
The upper low is currently over SE CA and is headed to the east. It will continue to bring northerly flow aloft to Srn CA through the day. At the sfc building sfc high pressure to the NNE will bring about 4 mb of offshore flow from the north and 1 to 2 mb from the east. The offshore flow and reinforcing upper level flow will bring low level advisory gusts (35 mph to 45 mph) to the mtns as well as the SBA south coast. Local gusts to 35 mph will affect portions of LA and VTA counties as well. The offshore flow and rising hgts will bring a warming and drying trend to entire area. Most areas will see a 4 to 8 degree bump up in temps today with max temps topping out in the 80s across the csts and upper 80s to mid 90s in the vlys.
For Wednesday and Thursday an east Pac ridge will build into the state and raise hgts to 588 dam. There will only be weak offshore flow Wednesday morning with onshore flow in the afternoon. By Thursday there will be onshore flow through the day. An eddy is forecast to spin up each evening which will likely bring some patchy low clouds to the LA beaches while the onshore flow to the east will create some morning stratus across the portions of the Central Coast. The weaker offshore flow on Wednesday will lead to 1 to 3 degrees of cooling across the csts and vlys, but the increased hgts will lead to about 5 degrees of warming for the mtns and far interior. Despite the better onshore flow on Thursday the increased hgts and subsidence from the upper will allow all areas to warm 2 to 4 degrees with the only exception being the Central Coast which will see little change. Look for 80s and and few 90 degree readings across the csts on Thursday with the vlys reaching the lower to mid 90s. These max temps are 4 to 8 degrees above normal.
(Fri-Mon), 29/228 AM.
As has been mostly the case for both August and September the forecast focus will be on the heat. A large dome of high pressure will sit atop of the state and bring 590 dam hgts to Srn CA. The ridge does break down on Monday but will only drop to 588 dam. The forecast problem lies in the sfc pressure gradients where there remains a large range of possibilities. Right now the most likely scenario is for there to be be 2 or 3 mb of offshore flow in the mornings and 1 mb of onshore flow in the afternoon. This would result in highs in the 80s and lower 90s across the csts and mid 90s to 102 degrees in the vlys. These kind of max temps are 10 to 15 degrees above normal. There is a 30 to 40 percent chc that there will be stronger offshore flow in the mornings and no onshore flow in the afternoons. This scenario would generate a long duration 3 day heat event with highs 90 to 100 across the csts and 100 to 110 degrees in the vlys. The vlys will have the typical low humidities assoc with offshore flow. There could be more humidity across the csts, however, if the offshore push is not that strong due to the high sea sfc temps. Heat headlines are a near certainty for this period the only question is weather they will be heat advisories or heat warnings.
There will be a few degrees of cooling on Monday as the ridge relaxes some, but max temps will remain 10 or more degrees above normal.
The EC-AI mdl remains very steadfast in its prediction that well above normal temps will persist through the 1st 2 weeks of October.
29/1705z.
At 1633Z at KLAX, the marine layer was 1200 feet deep with an inversion top at 2400 feet with a temperature of 23 degrees C.
High confidence in VFR TAFs for KPRB, KWJF, KPMD, and KSBA. There is a 15% chance for brief IFR cigs at KSBA after 13Z.
Moderate confidence in VLIFR conds at KSBP/KSMX tonight, with a 20-30% chance for VFR conds to prevail, higher at KSBP.
Moderate confidence in remaining TAFs. VFR conds expected through at least 06Z, then there is a chance for IFR-MVFR conds to return, highest chances for LA County coastal sites after 10Z.
Gusty winds will be common at all sites today.
KLAX, Moderate confidence in TAF. Gusty onshore winds will be common this afternoon and evening. There is a 20% chance for VFR conds to prevail. There is a 50% chance for east wind component reaching 8 knots between 10Z-18Z.
KBUR, High confidence in VFR TAF. 20% chance for IFR conds after 12Z tonight. Gusty northerly winds will be common through this evening.
29/837 AM.
High confidence in Small Craft Advisory (SCA) winds and steep seas affecting the outer waters into Wednesday morning with local Gale Force gusts will be possible this afternoon and evening for the outer waters south of Point Conception. Nearshore waters along the Central coast will see SCA winds and steep seas this afternoon and evening.
For the inner waters south of Point Conception, SCA winds are expected across much of the Santa Barbara Channel and the inner waters adjacent to Los Angeles and Orange Counties this afternoon into tonight.
Southerly swell from Polo (SSE) will continue to affect the region through this evening, decreasing fairly rapidly. These swells will create larger waves and surf nearshore, which could impact some south exposed harbor entrances.
Conditions are likely to improve to below SCA levels Wednesday into next weekend, except for occasional northwest SCA winds near Point Conception in the afternoon/evening hours.
29/837 AM.
Southerly swell from Hurricane Polo will continue to affect our coastline today. This swell timing will line up with very high tides though this morning. Some south-facing shores are more vulnerable because of the lingering erosion effects from Hurricane Marie earlier this month. The areas of most concern include Avalon, Long Beach, Malibu, and to a lesser extent Santa Barbara.
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 possible in the most vulnerable areas. Minor tidal overflow may affect west facing beaches due to very high tides.
Beach Hazards Statements (BHS) are in effect for Santa Barbara south coast through Wednesday. A Coastal Flood Advisory and High Surf Advisory are in effect for LA and Ventura through this afternoon. A BHS may need to be issued for the LA and Ventura coasts for Tuesday afternoon through Wednesday (lining up with Santa Barbara) due to the very high tides.
The East Pacific Hurricane Season is forecast to remain active, with with additional southerly swells and surf/coastal flooding impacts possible again next week as Tropical Storm Rachel is forecast to move northwest.
Ca, Coastal Flood Advisory in effect until 5 PM PDT this afternoon for zones 87-354-362-366. (See LAXCFWLOX). High Surf Advisory in effect until 5 PM PDT this afternoon 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 until midnight PDT tonight for zones 645-650-655. (See LAXMWWLOX). Small Craft Advisory in effect until 9 AM PDT Wednesday for zones 670-673-676. (See LAXMWWLOX).
