10/749 AM.
Temperatures will cool region wide through the weekend and into early next week. Tropical Storm Rachel is expected to track well south of Los Angeles County, but periods of light to moderate steady rain transitioning to showers with a low chance of thunderstorms is forecast from this evening into early next week. Another warm up with the potential for offshore flow is likely Wednesday into the weekend.
(tdy-Mon), 10/737 AM.
***UPDATE***
Tropical Storm Rachel is still forecast to track well south of Los Angeles.
Some light showers, mostly virga are dreaming over areas mainly south of Point Conception this morning. Mostly cloudy skies will dominate over the next 36 hours or so, and while there are some light showers now, we're still expecting the more moderate and steadier rainfall to occur from late tonight/early Sunday morning and continue into the afternoon as the mositure from Tropical Storm Rachel will be pulled in from an upper level low about 300-400 miles southwest of Los Angeles. The bulk of the rainfall is still expected to focus across Los Angeles County and potentially eastern Ventura County.
Then the second, colder upper low will drop down into California, bringing cooler temps and continuing the chance of rain across the entire region. A more showery pattern is likely.
A 5-10% chance of thunderstorms continues through Monday. As for rain totals and rates, the values below are still on track. The one exception is latest high resolution data is indicating that some hourly rain rates in the Eastern San Gabriel Mountains may slightly exceed 0.50 inches per hour, but still expecting rates to remain below any burn scar thresholds. There may be some locally higher rainfall totals in this area as well. At this point, still not seeing enough to warrant any sort of flood watches in our area.
***From Previous Discussion***
Overall, 00Z models in good synoptic agreement through the short term period. Main features of concern will be a couple of upper lows dropping down across the area as well as Tropical Storm Rachel. With respect to Tropical Storm Rachel, it will continue track far south of Los Angeles county.
With this developing pattern, main concern continues to be rain chances. The first upper low, currently southwest of Point Conception, will interact with Rachel later today through Sunday evening, bringing light to moderate showers to the area. At this time, the best chances and highest amounts will be across LA county with chances/amounts decreasing further north and west. By Sunday night, the second upper low will begin to move south across California and will impact the area Monday and Monday night. At this time, models differ on the exact track of this second low, but any model solution continues to indicate a threat of showers for all areas.
Some details to note: - PWAT anomalies, associated with moisture from Rachel, will be 150-300% of normal. - PWAT anomalies will decrease on Monday. - There will continue to be a 5-10% chance of thunderstorms through Monday. - Totals today through Tuesday: - LA County: generally 0.25-1.00 inches except 1.50-2.50 inches over the San Gabriel Mountains. - 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. - LA County is under Marginal to Slight Risk for Excessive Rainfall on Sunday.
A secondary concern in the short term will be winds, specifically across the mountains and deserts. At this time, widespread wind gusts, around advisory-levels. are likely on Sunday across the LA county mountains and the Antelope Valley. Winds elsewhere on Sunday will be breezy in many areas, but should remain below advisory levels.
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), 10/233 AM.
For the extended period, models are on the same general synoptic page, indicating dry conditions and a noticeable warming trend through Friday as a upper level ridge builds somewhere in/over the area. Models do indicate some increasing offshore pressure gradients Wednesday through Friday. This offshore flow will be the main reason for the warming trend across the area. As for actual winds, the forecast gradients and forecasted upper level support will likely generate a weak Santa Ana wind event Thursday/Friday with a chance of a moderate event. Will have to monitor this situation closely over the coming days.
10/0932z.
At 0900Z at KLAX, the marine layer was 600 feet deep. The top of the inversion was 2200 feet with a temperature of 24 degrees Celsius.
For 12Z TAF package, high confidence in KPMD and KWJF.
For all other sites, moderate confidence in 12Z TAFs. For sites north of Point Conception, timing of flight category changes could be +/- 3 hours of current forecast. For sites south of Point Conception, high clouds overhead are making for a chaotic stratus pattern. So, timing of any arrival or dissipation of CIG/VSBY restrictions could be +/- 3 hours of current forecasts.
KLAX, Moderate confidence in 12Z TAF. There is a 40% chance of MVFR CIGs 12Z-19Z. Timing of showers this evening and overnight could be +/- 2 hours of current forecast. No significant easterly wind component is expected.
KBUR, Moderate confidence in 12Z TAF. There is a 30% chance of MVFR CIGs 12Z-19Z. Timing of showers tonight could be +/- 2 hours of current forecast.
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). Beach Hazards Statement in effect through late tonight for zones 340-346. (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). 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).
