09/200 PM.
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 rain showers with a low chance of thunderstorms is forecast from Saturday evening into early next week. Another warm up with the potential for offshore flow is likely Wednesday into the weekend.
(Fri-Mon), 09/812 PM.
Evening satellite imagery starting to show Tropical Storm Rachel moving to the northeast. Tropical moisture moving into a nearby upper level low pressure system is beginning to develop thunderstorms in the diffluent area on the east side of the low. Tropical Storm Rachel is expected to track well south of Los Angeles. While we will not see direct impacts from Rachel in our area, we will still some impacts related to Rachel's influence.
On Saturday a weak upper low around 500 NM miles southwest of Point Conception is forecast to continue to move south, pulling in mositure from Rachel across southern California. By Saturday afternoon, precipitable water values increase to 1.3 to 1.5 inches. As this moisture interacts with some enhanced vorticity areas on Saturday, upper level diffluence shifting into our region, and some elevated instability, have introduced a slight chance of shower for our coastal waters on Saturday morning, then a slight chance of showers/thunderstorms for all areas coastal/land areas south of Point Conception by afternoon. This is also supported by high resolution QPF/reflectivity outputs for Saturday afternoon.
***From previous discussion ***
There is some sensitivity in terms of peak timing of rain chances, but best chances exist from early Sunday morning into the early afternoon hours. However, chances exist into Sunday night. There is a low (5-10% chance) of thunderstorms over eastern LA County during this period. Breezy onshore northwest to southwest onshore flow will be common area wide on Sunday, but at this point winds look to be below advisory levels.
A second, much colder upper low is then forecast to drop down though coastal California late Sunday into Monday morning. There is some disagreement on how far inland of California and and how far south this next upper low will track, but we have good confidence in some of the coolest temperatures Southwest California has experienced in quite some time. We also are fairly confident in more widespread chances of rain from early Monday through the late evening hours. There is still some uncertainty regarding rain totals and intensity, but at this point it appears that we will see fairly light rainfall from this secondary system. PWATs decrease fairly rapidly from 1.5 inches Sunday to 0.8 inches by Monday afternoon near Los Angeles. However, if the upper low tracks further south and just off the coast of California and southerly flow develops, there may be some enhanced precipitation totals (and rates especially over terrain) for areas south of Point Conception. There again is a 5-10% chance of thunderstorms anywhere on Monday. Once again depending on the track of this upper low there may be some advisory level wind gusts especially focused across the mountains early Monday morning. At this point confidence isn't high enough for any wind headlines.
For rain totals for both days our best estimate is between 0.25 and 1.0 inches, locally higher in the mountains, especially the Eastern San Gabriels. We're not expecting widespread freshwater flooding at this point, but some areas of minor roadway flooding is possible. The more significant impacts are likely going to come from the coastal flooding side of things, especially for south facing beaches in Los Angeles County. Please refer to our Marine Discussion and our CFWLOX products for more details.
(Tue-Fri), 09/200 PM.
Rain shower chances continue into Tuesday with only light rain expected. Then there is solid model agreement that the upper low will move to the east fairly rapidly. We will then dry out and likely see some increasing northerly flow. Wednesday will more or less be a transition period as we enter a pretty rapid warming trend which will becoming more apparent Thursday and Friday as a ridge (near 590 dam) builds in and offshore flow is forecast to develop. While there is a wide range of outcomes regarding the offshore flow, the most likely outcome is a weak to moderate Santa Ana Wind event.
10/0000z.
At 1722Z at KLAX, the marine layer was 900 feet deep. The top of the inversion was 2000 feet with a temperature of 23 degrees C.
High confidence in KWJF and KPMD. For all other sites, moderate confidence in TAFs as timing of flight category changes through the period could be +/- 3 hours of current forecasts, and there is a 20-40% chance that cigs may not develop at all where they are forecast.
KLAX, Moderate confidence in TAF. Timing of flight category changes could be +/- 3 hours of current forecasts, and there is a 20% of only a few hours if any of cigs developing tonight. No significant easterly wind component is expected.
KBUR, Moderate confidence in TAF. There is a 10% chance of BKN002-10 cigs forming between 12Z-15Z Sat.
09/840 AM.
For the Outer Waters, moderate to high confidence in current forecast. Today through Saturday morning, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. From Saturday afternoon through Monday morning, high confidence in a combination of SCA level winds and seas. 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. Today through Saturday morning, winds and seas are expected to remain below SCA levels. From Saturday afternoon through Tuesday, SCA level winds are expected (mainly in 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. Today through Saturday, high confidence in winds and seas remaining below SCA levels. For Sunday, there is a 60-80% chance of SCA level winds. For Monday through Tuesday, high confidence in winds and seas remaining below SCA levels except for a 50% chance of SCA level winds on Tuesday across the western half of the Santa Barbara Channel.
Periods of light to moderate showers is likely Saturday evening 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.
09/846 PM.
A Coastal Flood Warning is in effect for the beaches of Los Angeles County (including the Malibu Coast and Catalina Island), in effect through 3 PM Sunday. Highest impacts are likely for vulnerable south-facing beaches, especially Long Beach and Malibu, and damaging sea-water flooding of structures and beach roadways is likely near times of high tide, which 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 4 to 7 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 from 8 AM PDT Saturday through late Saturday night 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 from 8 AM PDT Saturday 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 Saturday to 3 AM PDT Sunday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 6 PM Saturday to 9 PM PDT Sunday for zones 650-655-676. (See LAXMWWLOX). Small Craft Advisory in effect from 6 AM Saturday to 9 PM PDT Monday for zones 670-673. (See LAXMWWLOX).
