textproduct: Los Angeles

SYNOPSIS

08/801 PM.

Temperatures across the region are expected to trend cooler Friday into Sunday and there will be an increasing chance of showers and thunderstorms due to moisture from Hurricane Rachel. These showers could persist into Tuesday, with another warming trend possible Wednesday through Friday.

LONG TERM (MON-THU)

09/213 AM.

For the extended period, 00Z models exhibit some noticeable disagreement, leading to relatively low confidence in the extended forecast. The GFS, and its ensembles, drop an upper low along the CA coast and over the area on Monday then move it eastward over the area and into the Great Basin on Tuesday and Wednesday. Conversely, the ECMWF, and its ensembles, drop the low over the Great Basin Monday and Tuesday, before ejecting it eastward on Wednesday and Thursday.

Forecast-wise, either model solution will generate a threat of showers across all areas Monday and Tuesday. Given the uncertainty of the pattern, forecast takes a middle ground. Rainfall totals on Monday and Tuesday are forecast to range between 0.10 and 0.25 inches for most areas with up to around 0.50 inches in the mountains. If the GFS solutions verifies, the rainfall totals would be on the higher side of that range. As for any thunderstorm threat, the GFS track of the upper low could give some mentionable chance of thunderstorms while the ECMWF solution would not. So, will any chances of thunderstorms under 10% at this time and see how things develop.

For Wednesday and Thursday, both models indicate increasing offshore pressure gradients. The ECWMF is stronger with the forecast gradients, indicating the potential for weak (to possibly moderate) Santa Ana winds. The GFS, with its weaker gradients, would indicate a weak Santa Ana at worst. Either way, with rising H5 heights and some amount of offshore flow, temperatures will be on the upswing Wednesday and Thursday.

AVIATION

09/1032Z.

At 1000Z at KLAX, the marine layer was 1100 feet deep. The top of the inversion was 3700 feet with a temperature of 25 degrees Celsius.

For 12Z TAF package, 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.

KLAX...Moderate confidence in 12Z TAF. Timing of flight category changes could be +/- 3 hours of current forecasts. No significant easterly wind component is expected.

KBUR...Moderate confidence in 12Z TAF. Timing of flight category changes could be +/- 3 hours of current forecasts.

MARINE

09/213 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, 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.

Widespread light to moderate rainfall 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.

BEACHES

09/213 AM.

A Coastal Flood Advisory is in effect through Tuesday afternoon for Los Angeles and Ventura Counties, while a Beach Hazards Statement (BHS) is in effect for the Santa Barbara South Coast and the Central Coast.

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 elevated surf and dangerous rip currents at times. Extremely high tides will be common each morning, peaking between 6.8 to 7.6 feet MLLW, highest further south. Additionally secondary high tides will peak each evening, likely most impactful through the weekend with tides reaching 5.5 to 6.5 feet MLLW.

While each day under the Coastal Flood Advisories or BHS should see fairly similar impacts, Sunday will likely see elevated impacts. Rapidly increasing wind speeds will likely add to the coastal flooding potential, creating a wind swell as well as elevating tides slightly. Additionally, if Rachel's track deviates a bit more to the north that would result in lower mean sea level pressure contributing to even higher water levels. If all these ingredients overlap on Sunday, a more significant coastal flooding event will be likely. This is a very narrow window, but there is a low chance for a targeted Coastal Flood Warning to be issued in southern Los Angeles County if all factors line up.

As this is a complex and evolving situation, please continue to monitor the forecast.

LOX WATCHES/WARNINGS/ADVISORIES

CA...Coastal Flood Advisory in effect until 2 PM PDT Tuesday for zones 87-354-362-366. (See LAXCFWLOX). Beach Hazards Statement in effect from Saturday morning through Monday afternoon for zones 340-346-349-350. (See LAXCFWLOX). PZ...NONE.