| Day | Date | High/Low | Forecast |
| Tue | 3rd | 81/66 | Sunny day. Clear evening. |
| Wed | 4th | 88/68 | Sunny day. Clear evening. |
| Thu | 5th | 95/71 | Sunny day. Mostly clear evening. |
| Fri | 6th | 96/72 | Mostly sunny day with some high clouds possible. Mostly clear evening. |
| Sat | 7th | 93/69 | Mostly sunny day with some mid/high clouds possible. Some evening mid/high clouds possible. |
Synopsis
Predicting temperatures near the coast, such as at UCLA, can be challenging on some occasions. Last week, a shallow marine layer helped keep daytime temperatures down more than the numerical models predicted (last Friday’s high was just 71 degrees). Another challenge comes this week, but in this case, it’s a question of whether a predicted, albeit weak, off-shore flow will permit temperatures to soar (even at some beaches).
All the models predict high pressure aloft will strengthen over the Southwest this week (already began yesterday). Although the magnitude of the high pressure shouldn’t get exceptionally strong, a predicted marginal, off-shore flow (peaking Friday morning) could permit some areas by the coast to reach 90 degrees (maximum in some valley locales may approach 115 degrees late this week). For the campus area, I’ve stayed close to the model consensus with regard to forecast temperatures. Should the off-shore flow fail to materialize, UCLA shouldn’t warm into the 90s. In fact, if today’s weak on-shore flow is accompanied by an intermittent, coastal eddy, temperatures shouldn’t vary much from today’s readings (still expecting plenty of heat for well inland areas though). If a full fledged, off-shore flow develops (just enough to stifle onset of any ocean breezes to late afternoon), UCLA may reach 100 degrees for a day (Thursday or Friday). That would the first such occurrence since 4 September, 2022 (104 degrees that day). Overnight low temperatures in many areas may not fall below 70 degrees during the height of the heat wave (some locales, including the campus, potentially may barely get down to 80 degrees).
High pressure aloft should begin moving east over the weekend. That should help end the marginal, off-shore flow. That, in turn, should begin a cooling trend. That cooling trend should be noticeable by the coast, but it should be much less so as one travels inland. The inland, coastal plain is likely to reach the 90s this weekend (triple digit heat for most coastal valleys). If today’s model consensus is right, the inland, coastal plain should fall back to the 80s beginning on Monday. There are some model solutions, however, showing a slower cooling trend next week. A return to seasonable temperatures may not occur till the second half of next week. There are a number of model solutions showing cooler than normal weather late next week and over the subsequent weekend. However, this is far from certain. Despite the arrival of autumn on the 22nd (astronomically speaking), September is known for some of the hottest weather of the year in southern California (weak off-shore flow events).
It’s not predicted be anything significant, but an increase in “monsoonal” moisture may occur late this week. Some “monsoon” moisture aloft already entered the southern mountain/eastern desert region over the Labor Day weekend (a few, afternoon, brief-lived thunderstorms occurred in spots). A little greater activity is possible this Friday afternoon (more isolated again over the weekend). Depending on how much moisture aloft moves into the Southland, there could be some mid/high clouds west of the mountains at times (no threat of showers likely, however).
Next issued forecast/synopsis should be on Monday, 9 September.