11/235 AM.
Moderate to damaging coastal flooding will likely continue through at least Tuesday. Periods of light to moderate rain and a low chance of thunderstorms will persist through Monday with below normal temperatures. Beginning Tuesday and continuing through the end of the week, weak to moderate offshore flow will bring warm and dry conditions to the area.
(tdy-Tue), 11/235 AM.
Overall, 00Z models in good synoptic agreement through the short term period. For the public side of things, two main concerns will be precipitation and winds.
With respect to rainfall, no significant changes to the forecast have been made. Currently, Rachel is south-southeast of LA County and is moving quickly to the north-northeast. As expected, moisture associated with Rachel is generating widespread light to moderate showers across eastern LA county this morning with widely scattered light showers elsewhere. By this afternoon, Rachel, and the bulk of its moisture, will be well northeast of the area. Although Rachel will be moving out of the picture, there will still be plenty of residual moisture hanging around this afternoon and tonight, before the moisture starts diminishing noticeably during the day on Monday. A sharp, upper level trough will move across the area this afternoon through Monday. Given the expected residual moisture, this trough will generate the threat of showers just about anywhere trough Monday night. By Tuesday, the trough will be east of the area as its parent upper low drops into the Great Basin.
Based on current observations and QPF forecasts, no major changes have been made to the expected precipitation totals. Through Monday night, LA County is expected to have widespread totals in the 0.25-1.00 inch range with amounts up to 2.00 inches possible across the San Gabriel Mountains. Elsewhere, rainfall totals will be noticeably lower, with amounts of 0.25 inches or less likely. With the upper level trough this afternoon through Monday, there will also continue to be a 5-10% chance of thunderstorms. Rainfall rates are expected to generally remain below 0.25 inches/hour. However, over the San Gabriel Mountains and associated with any thunderstorms, local rates around 0.50 inches/hour will be possible and could generate some minor hydrologic issues.
As for winds, rather gusty southwesterly winds are expected to develop across the mountains and deserts later this morning and continue through early Monday morning. Wind gusts of 35-50 MPH are likely with even local gusts around 60 MPH (especially across the desert foothills). So, current WIND ADVISORIES will remain in effect for the LA Mountains and Antelope Valley through tonight.
(Wed-Sat), 11/235 AM.
For the extended, 00Z models continue to exhibit good synoptic agreement through the period. At upper levels, ridge will build over the West Coast. At the surface, high pressure will settle over the Great Basin.
Forecast-wise, the above scenario will bring warm and dry conditions to the area. The combination of the upper level ridge and offshore surface gradients will bring a noticeable warming trend for all areas through Saturday. In fact by Friday and Saturday, moderate to locally major Heat Risk will be possible across the coastal plain and coastal valleys.
As for winds, all models indicate increasing offshore surface pressure gradients through the period. At the same time, models indicate some decent upper level wind support (925/850 mb) developing. So, there is increasing confidence in weak to moderate Santa Ana winds developing. At this time, the peak gradients and upper level wind support look to occur on Friday. Looking at the ensemble mean gusts, gusts around 40 MPH are indicated Friday morning at Camarillo and Newhall. So, there is a decent chance of moderate Santa Ana winds developing across Ventura/LA counties by Friday and Saturday. So, would not be surprised to see wind advisories issued for the Santa Ana wind corridor.
11/0935z.
At 0930Z at KLAX, there was neither a marine layer nor a marine inversion.
Overall, moderate confidence in 12Z TAF package. Moisture streaming northward from Tropical Storm Rachel will bring the threat of showers to all sites south of Point Conception through this morning. For this afternoon through tonight, there will be a threat of showers at all sites. Through the TAF period, there will be 30-40% chance of MVFR CIGs at all sites. Additionally, there is a 5-10% chance of thunderstorms through the period.
KLAX, Moderate confidence in 12Z TAF. There is a 40% chance of MVFR CIGs anytime during the TAF period. No significant easterly winds are expected.
KBUR, Moderate confidence in 12Z TAF. There is a 40% chance of MVFR CIGs anytime during the TAF period.
11/235 AM.
For the Outer Waters, moderate to high confidence in current forecast. Today through Monday, high confidence in a combination of Small Craft Advisory (SCA) level winds and seas. Additionally, there is a 20-30% chance of Gale force winds this morning. On Tuesday, there is a 40-60% chance of SCA level winds, especially around Point Conception. For Wednesday through Thursday, high confidence in winds and seas remaining below SCA levels.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Today through this evening, high confidence in a combination of SCA level winds and seas. For Monday, high confidence in winds and seas remaining below SCA levels. For Tuesday through Thursday, there is a 30-50% chance of SCA level winds in the afternoon and evening hours.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Today through this evening, high confidence in SCA level winds. For Monday through Wednesday, high confidence in winds and seas remaining below SCA levels for most area, but the only exception is the western half of the Santa Barbara Channel where there is a 50% chance of SCA level winds Tuesday afternoon and evening. On Thursday, there is a 30-40% chance of SCA level northeast winds from Ventura south to Santa Monica.
Periods of light to moderate showers are likely through Monday with the highest confidence today. There is a 10% chance of thunderstorms during the same time frame. While showers or thunderstorms are possible anywhere, the 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.
11/235 AM.
A Coastal Flood Warning is in effect for the beaches of Los Angeles County (including Long Beach, the Malibu Coast and Catalina Island) through 3 PM today. DAMAGING sea-water coastal flooding is likely today, especially near the morning high tide where anticipated tide levels are expected to be around 8 feet. The most likely areas for DAMAGING coastal flooding this morning will be vulnerable south-facing beaches due to the expected combination of very high tides around 8 feet (including additive effect of low barometric pressure and onshore winds gusting to 15 to 25 mph), high surf of 5 to 8 feet, and light to moderate rainfall. THERE IS GROWING CONFIDENCE THAT THE EXPECTED COASTAL FLOODING IMPACTS THIS MORNING FOR VULNERABLE SOUTH FACING BEACHES OF LA COUNTY COULD BE THE MOST SIGNIFICANT WE HAVE SEEN SO FAR THIS SEASON, INCLUDING THOSE SEEN WITH Marie.
For all other beaches and harbors of LA county, minor to moderate sea-water flooding will likely impact beaches and walkways, especially with the morning high tide which could cause local damage to the most vulnerable locations such as Venice and Long Beach. For all beach areas, significant erosion is expected. There is an increased risk of ocean drowning. Dangerous and life- threatening rip currents can pull swimmers and surfers out to sea. Large breaking waves can cause injury, wash people off beaches and rocks, and capsize small boats near shore. The projected high tides of around 8 feet for this morning would approach or exceed recent record tide levels for LA county. Large secondary high tides are also expected each evening.
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. In addition to the Coastal Flood Advisory for Ventura County, Coastal Flood Advisories have been added for the Central Coast and southern Santa Barbara coast. For Ventura county, there is the possibility of localized damage across low-lying areas during the morning high tide, along with the threat of significant sea spray and and water on sections of PCH between Point Mugu and Sycamore Cove.
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 this afternoon for zones 87-362-366. (See LAXCFWLOX). Coastal Flood Advisory in effect from 3 PM this afternoon to 2 PM PDT Tuesday for zones 87-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect until 6 AM PDT early this morning for zones 340-346. (See LAXCFWLOX). Coastal Flood Advisory in effect from 6 AM this morning to 10 PM PDT Monday for zones 340-346-349-350. (See LAXCFWLOX). High Surf Advisory in effect from 6 AM this morning 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 this morning to 10 PM PDT this evening for zones 354-362-366. (See LAXCFWLOX). Wind Advisory in effect until 5 AM PDT Monday for zones 378>383. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 9 PM PDT this evening for zones 645-650-655-676. (See LAXMWWLOX). Small Craft Advisory in effect until 5 PM PDT Monday for zones 670-673. (See LAXMWWLOX).
