30/113 PM.
Little change in weather conditions is expected through Thursday with temperatures 4-8 degrees above normal. Areas of morning low clouds and fog are possible near the coast as well. A major and long lasting heat wave will begin Friday and last through all of next week at least with with dangerously hot temperatures.
(tdy-Sat), 01/249 AM.
***A VERY DANGEROUS AND LONG LASTING HEAT WAVE FRIDAY THROUGH AT LEAST NEXT WEEK AND LIKELY EXTENDING INTO THE SECOND WEEK IN OCTOBER***
Today will hint at the upcoming heat wave. An upper high will slide over Srn CA and raise hgts to ~589 dam. There will be near neutral sfc flow in the morning and weak onshore flow in the afternoon. An eddy has brought low clouds to most of the csts and some of the lower vlys. The marine layer is shallow enough across SLO and SBA counties to allow for some dense fog to form. The marine layer and weak onshore flow will keep coastal temps similar to ydy. The hgts rises and subsidence from the building upper high will bring 3 to 5 degrees of warming to the vlys mtns and far interior. Most temps across the csts/vlys will be 3 to 6 degrees above normal. Look for 10 degrees above normal temps further inland.
The well advertised long duration heat wave kicks off on Friday. Weak offshore flow will develop in the morning, but it will not be strong enough to prevent some marine layer low clouds from forming. The upper high will stretch over Srn CA and Srn NV with 590 dam. The weak offshore flow and high pressure aloft will team up to produce 4 to 8 degrees of warming across the csts and vlys. Most coastal areas will see highs in the mid and upper 80s except the LA cst will likely see plenty of high in the lower to mid 90. The vly temps will soar into the upper 90s to 105 degrees. These max temps 10 to 15 degrees over normal will pose heat health hazards to the area. An extreme heat watch goes into effect for all of the csts and vlys south of Pt Conception and will continue through the short and long term periods.
Saturday will feature even stronger offshore flow in the morning (but still weak enough to not produce much if any canyon winds) and even weaker onshore flow in the afternoon. This will make Saturday the hottest of the next 7. There will be an additional 2 to 4 locally 6 degrees of warming across the csts and vlys. This warming will push most cstl temps into the 90s and and vly temps to 100 to 107. Max temps will end up 15 to 20 degrees over normals.
The offshore flow will mean that this heat will feature much less humidity than the previous heat events in August and September.
The Central Coast will have warmer than normal temps but will remain just under heat headline criteria. Still residents there should take heat precautions when exercising or working outdoors.
(Sun-Wed), 01/249 AM.
The xtnd forecast shows little change in the heat. There may be a couple degrees of cooling from Saturday's very hot numbers but no where near enough to reduce the heat danger. The combination of light offshore flow and high pressure aloft will allow for little day to day change in max temps Mon Tue and Wed. Max temps during this period will mostly be 10 to 15 degrees above normal. Weak offshore flow overnight and a strong inversion likely around 900 ft will keep overnight lows above normal as well limiting the body's ability to recover overnight.
Another heat related problem will be an increase in humidity courtesy of Hurricane Rachel. The increased in humidities will arrive Monday and will likely continue through Wednesday. Rachel is forecast to track to the west it will send ocean swells along with the aforementioned moisture . There's even a small (5-15) percent chance of a mtn shower or thunderstorm in the afternoons.
Even through this heat wave will not likely produce record heat it will still be very dangerous due to the prolonged duration of the event. The relentless heat will have a hazardous wearing down effect on people esp the very young and old.
One bit of good news the long range mdls are now showing cooler temps arriving a few days earlier than with the fcst ydy. Today's mdls show improving conditions starting around the 10th rather than the 13th.
01/0948z.
At 0505Z at KLAX, the marine layer was 1100 ft deep. The top of the inversion was near 3000 ft with a maximum temp of 25 C.
High confidence in VFR TAFs for KWJF and KPMD.
Low confidence in KBUR & KVNY TAFs with a 40 percent chc of no low clouds (or only for a very brief time)
Moderate confidence in remaining TAFs. Timing of change groups may be off +/- 2 hours. CIG height accuracy +/- 300 ft of fcst. There is a 30 percent chc that KSBA will not see vis AOB 3/4SM.
KLAX, Moderate confidence in TAF. VFR conds may arrive as late as 2000Z. There is a 30 percent chc of OVC012 conds aft 15Z. No significant east wind component expected.
KBUR, Low confidence in TAF. There is a 40% chance of no low clouds or only a brief 30 to 40 minute period of low clouds.
01/244 AM.
Lingering swell near 10 feet for the far northern outer waters is expected to trend downwards going forward. Local areas of Small Craft Advisory Level (SCA) gusts are possible each afternoon and evening through at least Saturday, for areas around Point Conception, off the coast of Point Dume, and across the San Pedro Channel. Beside the aforementioned areas, quiet marine conditions are expected for the rest of the coastal waters.
30/801 PM.
Beach Hazards Statement has been allowed to expire.
While we will get a break from the coastal flooding concerns for the rest of the week, another hurricane swell (from Rachel) will likely bring a larger-than-Polo south swell to southern California for the early to middle part of next week. Thankfully tides at that time will not be extreme, but they should be around 6.5 feet which is high enough to cause some concern, but it all depends on how big the surf ends up. Stay tuned for future updates.
Ca, Extreme Heat Watch in effect from Friday morning through Thursday evening for zones 38-87-88-349>358-362-366>375-548-550. (See LAXNPWLOX). PZ, NONE.
