It is Too. Damn. Hot.

Our never-ending summer continues.

Friday, Saturday and Sunday, October 9-11, were all above 100 degrees in downtown Los Angeles. If you think this was pretty rare, you're right! Sure, sometimes it's hot in the fall, especially if there is a Santa Ana event. But this back-to-back string of three 100-degree days was the first time in 25 years that Los Angeles has experienced 3 such days in a row, and only the second time ever that this has occurred in October. But what has truly been extraordinary and, in my observation, largely unprecedented, are the extremely warm nights. This morning (Monday, October 12) the thermometer only made it down to 73 degrees. For context, the average low for October 12 is 60. In 3 days that average number dips to 59. That means that this morning was 13 degrees above normal. But the icing on the cake is that the past THREE mornings have all been above 70 degrees. And, since September 1, 13 mornings have had low temperatures above 70. This, coupled with 17 days with high temperatures above 90, has given us one of the warmest early-fall stretches in history. (Downtown LA is averaging +6F above normal for that period).

Here is a bar plot I've made showing the difference between the average daily temperature and the "normal" values. All but 4 days since September 1 have been above normal; most, WELL ABOVE normal. 

TO make things even weirder, two of the periods that exhibited below-normal temperatures coincided with extremely rare early-fall rain events (Sept 15-17 and October 4-6).

Just to give you an idea of how warm it is, here is a plot of yesterday's hourly temperature vs. the average hourly temperatures for October 11. Insane.

The other component to this exceptionally weird fall is the rainfall we've received so far. As of this writing, Downtown LA has picked up 3.22" of rain so far, putting us 2.70" above "normal", and the rainy season hasn't even really started yet!

To top it all off, there is another chance of rain this week - with possible showers and thunderstorms Wednesday through Friday.

But, what about El Niño?

So, what's going on with El Niño? Well, we're still on track for one of the strongest El Niño's in history. Sea surface temperatures in the NINO3.4 region (the region that NOAA and other agencies use to "track" El Niño are now around +2 degrees Celsius. The only stronger El Niño for this time of year was the 1997-98 El Niño that brought flooding rains to Orange County (December 1997) and Los Angeles (February 1998).

People keep asking me - "when" will El Niño hit? El Niño is not one singular storm. It is a climate phenomenon of the Eastern Pacific that has strong teleconnections with weather in other parts of the world. For example, in Australia and Indonesia, El Niño brings drought. In fact, Indonesia and Southeast Asia is in the midst of an historic drought right now. 

Here is a map showing the average sea surface temperature anomalies ending October 3. That tongue of red and orange above-normal temperatures in the Eastern Pacific is "El Niño". And, as Bill Patzert put it - the atmospheric and oceanic conditions are now such that this El Niño is "too big to fail"

The reason this El Niño is on a runaway course to Hall of Fame status is because the westerly wind bursts (WWBs), of which I have previously talked at length, are now dominating the entire Pacific, with strong westerly anomalies covering much of the equatorial Pacific. These westerly winds help push warmer Pacific water up against the S. American coast, sustaining the El Niño.

Model forecasts from mid-September now give us a 100% chance of El Niño continuing through March (at least), with NINO3.4 temperatures peaking near +2.5C!

The moral of the story: We can probably expect a very wet winter. NOAA now gives us a 60% chance of above-normal rainfall and only 7% chance of below-normal.

Mika ToscaComment