25/215 AM.
Dry and warm conditions will continue through the first half of this week. Cooler conditions will follow, with a growing potential for a storm system towards the end of the week and into next weekend.
(tdy-Tue), 25/845 AM.
***UPDATE***
On track for quiet weather for the beginning of the week with gradual cooling almost every day. No changes made to the forecast.
Focus for today will be to provide an update on the late week storm that may impact Halloween festivities.
***From Previous Discussion***
Overall, latest models in good synoptic agreement through the short term period. At upper levels, weak ridge will move across the area tonight/Sunday with broad cyclonic flow developing on Monday and Tuesday. At the surface, a general weak diurnal flow will prevail through Monday with weak onshore flow on Tuesday.
Forecast-wise, relatively benign weather is expected through the short term period. With the gradual return of onshore pressure gradients, the marine layer should start to become more established from night-to-night across the coastal plain. Otherwise, skies are expected to remain mostly clear through the period.
With respect to winds, the weakening of the offshore flow the last couple of days will keep any offshore winds rather weak and localized tonight through Monday. On Tuesday, more widespread onshore winds will return to the area, but speeds will remain well below advisory levels.
Finally as for temperatures, there will be minor day-to-day changes through Monday, mainly at the whims of the onshore flow and marine influence. On Tuesday, will expect some slight cooling for most areas with the uptick in onshore flow.
(Wed-Sat), 25/216 AM.
For the extended, latest models continue to exhibit a rather broad synoptic agreement, but differ in the details. At upper levels, a low will develop over the Pacific Northwest on Wednesday/Thursday. On Friday and Saturday, the GFS continues to drop the low south along the coast while the ECMWF keeps over the Pacific Northwest (resulting in a sharp trough sweeping across the area).
Overall, either solution indicates a wet and unsettled Halloween weekend for Southern California. At this time, there is high confidence in measurable rainfall for most, if not all, of the area Friday through the weekend. However, confidence in timing of rainfall and totals remain very low. The latest 12Z/18Z runs have backed off on totals just a bit with even the run total QPF on the ensembles decreasing. Previous estimates of totals from 0.50 to 2.00 inches are still in play, but totals, in the end, could be more or less than that range.
The uncertainty in this pattern will be a challenge over the coming days. So, the forecast will likely change from one day to the next. However, residents should expect Halloween activities to be impacted by rainfall to some level. Stay tuned for the latest details about this upcoming storm.
25/1541z.
At 15Z at KLAX, there was a surface-based inversion. The top of the inversion was 2400 feet with a temperature of 19 degrees Celsius.
For 18Z TAF package, high confidence in CAVU conditions through the period for KSBA, KOXR, KCMA, KBUR, KVNY, KPMD and KWJF.
For KSBP, KLAX, KLGB and KSMO, there is a 10-20% chance of LIFR/VLIFR conditions 08Z-16Z.
For KSMX, there is a 50% chance that CIG/VSBY restrictions do not develop tonight.
KLAX, High confidence in 18Z TAF as CAVU conditions are likely through the period. There is a 10-20% chance of IFR/VLIFR conditions 10Z-17Z. No significant easterly wind component is expected.
KBUR, High confidence in 18Z TAF as CAVU conditions are expected through the period.
25/841 AM.
For the Outer Waters, moderate to high confidence in current forecast. Through tonight, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. For Monday through Wednesday, high confidence in winds increasing to SCA levels. On Thursday, there is a 50% chance of SCA level winds continuing.
For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. Through tonight, high confidence in winds and seas remaining below SCA levels. For Monday through Tuesday, there is a 50-60% chance of SCA level winds in the afternoon and evening hours. For Wednesday through Thursday, the chances for SCA level winds diminish to 20-30%.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Today through Thursday, 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 50-60% chance of SCA level winds Monday afternoon and night.
Dense fog is likely to form over portions of the coastal waters over the next 48 hours, but low confidence on exactly when and where.
A significant storm system will impact the area sometime in the late Thursday through early next week timeframe. There is a wide range of outcomes, but there is at least a low threat of a 12-24 hour period of strong winds and step seas.
25/216 AM.
Very high tides between 7.5 and 8.0 feet (roughly 1.0-1.5 feet above astronomical predictions) are expected during the morning hours of Sunday through Thursday over all coastal areas, with the highest towards Los Angeles County. Monday through Wednesday could produce the highest on record (current record at San Pedro is 7.93 feet set on Jan 10, 2005 with records going back to 1924).
Minor coastal flooding is likely purely based on the high tides. While these tides might be the highest of all-time, similar extreme tides in the past tell us that coastal communities should expect shallow flooding of harbor walkways, beach parking lots and bike paths. With swells and surf on the lower-end during these extreme tides (2-3 feet), the threat of more significance/damaging impacts should be limited to the most vulnerable areas that have little-to-no sandy beach left and have already seen water damage.
With that said, these is a small change for more elevated surf on south-facing shores around Wednesday as waves from a southern Hemisphere storm arrive. The majority of computer projections keep this wave energy on the small side, but a couple are a little larger.
With all of these considerations in play, Coastal Flood Advisories are in effect Sunday through Thursday. There is a low potential for targeted Coastal Flooding Warnings if a larger swell develops and produces elevated surf on top of the very high tides.
Ca, Coastal Flood Advisory in effect until 1 PM PDT Thursday for zones 340-346-349-350-354-362-366. (See LAXCFWLOX). PZ, NONE.
