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), 25/216 AM.
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.
25/0917z.
At 09Z over KLAX, there was no marine layer and no inversion.
High confidence in VFR conditions at all TAF sites through at least Sunday, except a 20% chance of LIFR FG near KSMX 12-16Z. Chances for LIFR/IFR ceilings Monday 10-16Z at KPRB 30%, KSBP 20%, KSMX 40%, KLAX 20%, KLGB 20%.
KLAX, High confidence in VFR conditions, except for a 20% of LIFR/IFR conditions Monday 12-16Z. High confidence in any east winds staying under 08 knots.
KBUR, High confidence in VFR conditions through at least Monday with typical winds.
25/214 AM.
High confidence in fairly benign conditions through early Monday. Small Craft Advisory (SCA) winds likely to form over most waters Monday afternoon, including the nearshore waters. SCA winds will retreat to the typical outer waters for Tuesday and Wednesday.
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.
