05/230 AM.
A major and long lasting heat wave will to persist through at least Thursday with dangerously high temperatures. Friday into Sunday, temperatures will trend cooler each day and there is a small chance of showers and thunderstorms due to moisture from distant Hurricane Rachel.
(tdy-Wed), 05/905 AM.
***UPDATE***
The heat wave continues. However, there is a small ray of hope that at least the beaches and up to a few miles inland may be as much as 5-10 degrees cooler today as offshore gradients have weakened by almost a millibar. Most areas are trending cooler so far this morning but by afternoon expecting most locations away from the immediate coast to be very close in temperature to yesterday. And very little change now through at least Thursday.
***From Previous Discussion***
Very little change in the days 1 to 3 forecast with the dangerous heat wave continuing through the period and beyond. Weak upper level high pressure with hgts around 589 dam will be overhead through the period. At the sfc there will be offshore flow in the morning and likely persisting into the afternoon (the mdls have been over forecasting the onshore flow in the afternoon).
Record or near record heat will persist. Most highs across the csts and vlys will be 90s to 104 degrees both today and Tuesday. Areas south of Pt Conception are forecast to cool some with a slightly better sea breeze, but at the same time the Central Coast will warm to 95 to 104 degrees as some offshore flow develops there. Even the beaches will give little relief with highs there in the upper 80s. These highs are 15 to 22 degrees over normal
Overnight lows will remain warm as well. Most lows will only dip to the upper 60s to mid 70s. There will be even be some low in the 80s in the mountains and foothills right at the top of the inversion.
All of the csts/vlys as well as many mtn and inland areas are under heat advisories and extreme heat warning through Thursday. Please see the product LAXNPWLOX for all of the details.
(Thu-Sun), 05/229 AM.
Some coastal cooling is forecast for Thursday esp across the Central Coast. This cooling is dependent on the gradient forecast being correct and there is a 30 percent chc that the cooling will not be as much as forecast. Whatever the cooling it will not be enough to end the heat threat and all heat warnings and advisories will continue into the evening.
There is good consensus that on Friday the upper high will be replaced by weak cyclonic flow and hgts will fall to 583 dam. Most importantly there will be onshore flow to the east and only weak offshore flow from the north. Highs will still be above normal with 80s and lower 90s across the csts and 90s in the vlys. A few areas in LA county may still need heat advisories, but overall it will be a warm but not dangerously hot day.
Actual troffing moves into the state on Saturday. Onshore flow will increase as well. Marine layer stratus will likely begin to form across some of the coasts. Max temps will drop 4 to 8 degrees across the board. Even with this cooling most max temps will end up 3 to 6 degrees over normal.
The moisture from Hurricane Rachel will begin to move into the area on Sunday. It will produce a 20-30 percent chc of showers mostly over LA county and points south. Continued troffing and onshore flow will bring a more robust marine layer cloud pattern and an additional 4 to 8 degrees of cooling. This cooling will bring a return of blo normal max temps.
Swell from Hurricane Rachel will likely arrive Tuesday.
05/0930z.
At 0822Z at KLAX, there was no marine layer. There was a sfc based inversion with a top at 800 ft with a temperature of 32 C.
Moderate confidence in TAFs for KSMX with a 30 percent chc of VLIFR conds 13Z-16Z. Fair confidence in TAF fog KSBP with a 15 percent chc of VLIFR conds 13Z-16Z.
High confidence in the remainder of the CAVU TAFs.
KLAX, High confidence in CAVU TAF. Good confidence that any east wind component will remain below 7kts.
KBUR, High confidence in CAVU TAF.
05/207 AM.
Generally quiet conditions are expected across the coastal waters through the forecast period. Localized Small Craft Advisory (SCA) gusts may occur each afternoon and evening between Point Conception and San Nicolas Island, off the coast of Point Dume, and across the San Pedro Channel. Winds over the outer waters will begin to increase Wednesday night through Friday with a 30% chance of SCA gusts at times, mainly during the afternoon to evening hours.
Night through morning dense fog may affect portions of the coastal waters west of the Channel islands and Point Conception through Thursday.
Ca, Extreme Heat Warning in effect until 8 PM PDT Thursday for zones 38-87-88-349>358-362-366>375-548-550. (See LAXNPWLOX). Beach Hazards Statement in effect from Tuesday afternoon through Friday evening for zones 87-354-362-366. (See LAXCFWLOX). Heat Advisory in effect from 10 AM Wednesday to 8 PM PDT Thursday for zones 340-346. (See LAXNPWLOX). Heat Advisory in effect until 8 PM PDT Thursday for zones 341>345-347-348. (See LAXNPWLOX). PZ, NONE.
