10/1054 AM.
Tropical Storm Rachel is expected to track well south of Los Angeles County, but moderate to damaging coastal flooding impacts are very likely to continue into at least early next week. Periods of light to moderate rain/showers and a low chance of thunderstorms exists into early next week, peaking Sunday. Temperatures will cool region wide through the weekend and into early next week. Another warm up with the potential for offshore flow is likely Wednesday into the weekend.
(tdy-Mon), 10/1054 AM.
Tropical Storm Rachel is still forecast to track well south of Los Angeles. The most significant impacts over the short term will almost certainly be due to coastal flooding. Please refer to Beaches section as well as CFWLOX for further details on coastal flooding issues.
An upper level low pressure system siting about 450 miles southwest of Los Angeles will be responsible for quite a bit of cooling today thanks to cooler air aloft as well as pretty widespread cloud coverage and some increasing onshore flow. There remains a slight chance of showers and a 5-10% chance of thunderstorms across the area through this evening, mainly focused south and east of Point Conception. Best chances exist in Los Angeles and Ventura Counties, with lower chances westward. However as the upper low moves to the east tonight, it will tap into more of Rachel's moisture as it approaches the northern Baja California Coast, bringing a likely chance of fairly steady light to moderate rain across Los Angeles and Ventura Counties through Sunday morning and into the afternoon hours. Another upper level low will drop down through California on the heels of the previous low, which will turn our steadier rainfall into a more showery pattern Sunday evening through Monday.
As far as rainfall goes, it appears the majority of our rainfall totals will come from the "first" system from late tonight into Sunday afternoon. In general we are expecting light to moderate rainfall totals and rates. Further details on the rain are below.
We are also expecting fairly breezy conditions for much of southwest California, especially in the mountains and deserts of eastern Los Angeles County. There will be a very sharp uptick in onshore pressure gradients Sunday morning along with the upper level influence of the second upper low dropping down south. A wind advisory has been issued for the San Gabriel Mountains as well as the Antelope Valley for Sunday, with gustiest winds expected during the afternoon through late evening hours.
Otherwise, much cooler temps will bring a relief to many after a long stretch of very hot weather.
Some details to note: - PWAT anomalies, associated with moisture from Rachel, will be 150-300% of normal. - PWATs will decrease on Monday. - There will continue to be a 5-10% chance of thunderstorms through Monday. - Rain totals today through Tuesday: - LA County: generally 0.25-1.00 inches except 1.50-2.50 inches over the San Gabriel Mountains (locally 3.00). - Ventura County: generally 0.10-0.50 inches with locally higher amounts possible over the mountains. - SBA/SLO Counties: generally under 0.25 inches. - Rainfall rates: generally under 0.25"/hour, but local rates up to around 0.50"/hour will be possible for LA County. Some recent higher resolution guidance suggests some rates in the Eastern San Gabriels may slightly exceed 0.50"/hour. - LA and Ventura Counties are under Marginal to Slight Risk for Excessive Rainfall on Sunday.
As has been stressed over the last few days, any changes in the track of Tropical Storm Rachel could bring noticeable changes to the expected rainfall for the area. So, stay tuned for the latest details.
(Tue-Fri), 10/1054 AM.
Wednesday will be more or less be a transition day from the cooler, active pattern to a warming and drying trend which will likely continue into the weekend. An upper level ridge of high pressure will build over the area and by Thursday we could see 500 mb heights reach 585-590 dam. Offshore flow is also poised to develop and these features will combine to bring this rapid warming and drying to southwest California. Widespread moderate heat risk is likely for the coasts and coastal valleys Thursday through the weekend, with low chances of major heat risk. The magnitude of temperatures will likely depend on the magnitude of the offshore flow, but a weak to at least locally moderate Santa Ana Wind event is likely.
10/1824z.
At 1724Z at KLAX, the marine layer was 1000 feet deep. The top of the inversion was 1500 ft with a temp of 23 degrees Celsius.
Moderate confidence in TAFs. For sites north of Point Conception, timing of flight category changes could be off by +/- 3 hours. For sites south of Point Conception, a few showers may occur between 19-22Z today. Then rain timing in TAF may be off by +/- 3 hours, with heavier periods of rain possible. Highest chances for rain will be Sunday morning. There is a 10% chance of tstorms through the period.
KLAX, Moderate confidence in TAF. A few showers are possible between 19-22Z today. Otherwise, timing of showers this evening through tomorrow could be +/- 3 hours of current forecast, with heavier periods of rain possible. There is a 10% chance of tstorms through the period. Bkn015-025 may be associated with rain. No significant easterly wind component is expected.
KBUR, Moderate confidence in TAF. A few showers are possible between 19-22Z today. Otherwise, timing of showers this evening through tomorrow could be +/- 3 hours of current forecast, with heavier periods of rain possible. There is a 10% chance of tstorms through the period. Bkn015-025 may be associated with rain.
10/919 AM.
For the Outer Waters, moderate to high confidence in current forecast. High confidence in a combination of at least SCA level winds and seas during this period, however lower confidence in winds Sunday. Winds will increase to Small Craft Advisory (SCA) levels today, potentially lasting into Sunday night. On Sunday, there is a 30% chance of Gale Force winds early in the morning, then there is a 40% chance that winds drop below SCA levels Sunday evening through Monday. However, steep seas of 10+ feet will build this afternoon and last into early Monday morning. On Tuesday, there is a 50% chance of SCA level winds around Point Conception with winds remaining below SCA levels elsewhere.
For the Inner Waters north of Point Sal, high confidence in current forecast. Winds and seas are expected to remain below SCA levels through this morning. From this afternoon through Tuesday, SCA level winds are expected (mainly during the afternoon and evening hours) with seas approaching SCA levels on Sunday and Monday.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Through this afternoon, high confidence in winds and seas remaining below SCA levels. From this evening through Sunday evening, there is a 60-80% chance of SCA level winds. For Monday through Wednesday, high confidence in winds and seas remaining below SCA levels for most of the southern Inner Waters. The only exception will be the western half of the Santa Barbara Channel with a 50% chance of SCA level winds late Tuesday afternoon through Tuesday evening.
Periods of light to moderate showers are likely today through Tuesday, with highest confidence for Sunday-Monday. There is a 10% chance of thunderstorms during the same time frame. While showers or thunderstorms are possible anywhere, highest chances exist south of Point Conception.
Long period swell from the west and the south are affecting the coastal waters, and can create a confused sea state. This can make boating more challenging and dangerous, especially for small vessels.
10/918 AM.
A Coastal Flood Warning is in effect for the beaches of Los Angeles County (including the Malibu Coast and Catalina Island) through 3 PM Sunday. Highest impacts are likely for vulnerable south-facing beaches, especially Long Beach and Malibu, with damaging sea-water flooding of structures and beach roadways likely near times of high tide. High tides are expected to range between 7.3 and 7.5 feet this weekend.
There is the potential for additive factors to the water levels on Sunday as some computer model projections are showing lower atmospheric pressure values (somewhere between 995 and 1005 mb) due to Rachel passing to our south and east, as well as the possibility of enhanced southwest to west onshore winds over the coastal waters near the time of Sunday morning high tide. There is still some uncertainty in these additive factors due to the timing of Rachel's track in relation to the high tides on Sunday morning. But we can expect water levels to be at least 7.3 to 7.5 feet across LA county during the Sunday morning high tide, with the potential for water levels to reach 8 feet if the low pressure/onshore wind components materialize near time of high tide.
As a result, Sunday has the highest risk for damaging coastal flooding (especially Long Beach and Malibu areas). The Coastal Flood Warning may be extended past Sunday, or converted to a Coastal FLood Advisory through Tuesday. High surf of 5 to 8 feet is also expected with locally higher sets possible Sunday, along with strong/dangerous rip currents.
For beaches from Ventura County northward, minor to moderate coastal flooding will be likely near times of high tide as well as periods of elevated to high surf and strong rip currents. Depending on the track of Rachel, there is a small chance (20 percent) that Ventura County will need to be upgraded to a Coastal Flood Warning. Please see CFWLOX for additional details.
A very complex series of swells from the south, west, and northwest will impact our coastlines into at least early next week. Energy from Tropical Storm Rachel, southern hemisphere swells, northwest swells, and local wind swells will add up with each other to produce the aforementioned coastal impacts. Please continue to monitor the forecast.
Ca, Coastal Flood Warning in effect until 3 PM PDT Sunday for zones 87-362-366. (See LAXCFWLOX). Coastal Flood Advisory in effect from 3 PM Sunday to 2 PM PDT Tuesday for zones 87-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect through late tonight for zones 340-346. (See LAXCFWLOX). Coastal Flood Advisory in effect from 6 AM Sunday to 10 PM PDT Monday for zones 340-346-349-350. (See LAXCFWLOX). High Surf Advisory in effect from 6 AM Sunday to 10 PM PDT Monday for zones 340-346. (See LAXCFWLOX). Beach Hazards Statement in effect through Tuesday afternoon for zones 349-350. (See LAXCFWLOX). Coastal Flood Advisory in effect until 2 PM PDT Tuesday for zone 354. (See LAXCFWLOX). High Surf Advisory in effect from 6 AM to 10 PM PDT Sunday for zones 354-362-366. (See LAXCFWLOX). Wind Advisory in effect from 5 AM Sunday to 5 AM PDT Monday for zones 378>383. (See LAXNPWLOX). PZ, Small Craft Advisory in effect from 3 PM this afternoon to 3 AM PDT Sunday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 6 PM this evening to 9 PM PDT Sunday for zones 650-655-676. (See LAXMWWLOX). Small Craft Advisory in effect until 9 PM PDT Monday for zones 670-673. (See LAXMWWLOX).
