What's Behind San Diego's Crazy Weather?

MAUREEN CAVANAUGH: This is KPBS Midday Edition, I am Maureen Cavanaugh. Forecasters are predicting another hot humid week for San Diego. It is not exactly Florida, but it is not the kind of weather we're used to in the summer. Our daytime highs have exceeded the average for each day the last couple of months, and there was rain on the coast in August. On top of all of this, big weather questions remain, what is the likelihood for Santa Ana conditions this fall, and will be or not we get that drought busting El NiÒo? I like to welcome my guests, Alex Tardy and Alexander Gershunov. Alex, what are the conditions that you would say characterize summer weather so far? ALEX TARDY: So far we have had a humid summer, but what has been unusual is that we have enough moisture and instability that we brought understands only to the coast, not just one weekend, but twice. So we have seen some good rain in our typical places, and too much rain unfortunately. We saw widespread flash flooding and damage in San Bernardino county, debrief flows, vehicles thrown into the creeks. What is really unusual is the temperatures. We have been above normal record warmth since January. This year, no matter where you are, it has been above normal. That includes water temperatures as well. MAUREEN CAVANAUGH: What about the community? Is that people seem to be talking about the most, they basically say that is not typical for San Diego. Is that really not typical for San Diego summer? ALEX TARDY: It's a typical to see it for so many months during summer. We typically have a few summer months will be humid, but the accommodation between the most trendy atmosphere coming from California Baja and also the sea surface temperatures, that is elevated and above normal. You have to look at the fact our though temperatures and high temperatures, even when you average them together, they been much of of record warmth for all locations. That's probably what people have been noticing. MAUREEN CAVANAUGH: Alexander, you studied long-term climate change, and earlier this year you're talking with us about the national climate assessment that was released. What were the most powerful trends identified for our region in the southwestern United States? ALEXANDER GERSHUNOV: The things we really notice with the very big trends in heatwave activity. It's not just temperatures, it's also the change of the flavor of heat waves, where heat waves are more humid. That keeps the nighttime temperatures much higher than they used to be. MAUREEN CAVANAUGH: I think it is difficult for people to see climate and weather together, the excess humidity and the increase in dry drought conditions. How do those two jive together? ALEXANDER GERSHUNOV: Climate is the statistics of weather. Weather is what makes climate, but on the other hand, there is some low-frequency large-scale types of variability in the earth system that also affect the with weather develops. For example, these he waves that we have been having lately, they are typically caused by situation that brings air from the South, and just to the south of us, the sea surface temperature west of Baja California has been warming more than the global ocean, which is also been warming in the last few decades. The air brought in by the extreme conditions that cause heat waves, tends to be more humid as well as warmer. MAUREEN CAVANAUGH: You have also done studies about the increase in heat in our nighttime temperatures could do to people who are not used to it along the coast. ALEXANDER GERSHUNOV: Extreme events are always stream compared what we are used to, compared with his normal. In California, we are used to high temperatures when it is dry. The hea waves that are happening more and more often that are humid are very unusual, and people are not used to that. The cooling that we expect at night during heat waves has not really materialized in the few events that we have had recently. That is taking people by surprise, to the extent of making people sick and some people dying as well. MAUREEN CAVANAUGH: So it increases a person's health problems? ALEX TARDY: That is correct. It is a heat health impact issue. We actually measure humidity by dewpoint temperature. That is the temperature that you have to call the air down to reach 100% situation. When you start seeing dew points the upper 60s and low 70s, it is more like Florida. That is stress on your body. Your body has a lot of trouble cooling down using its natural abilities. Cooling is not as efficient and that can cause heat stress. MAUREEN CAVANAUGH: Did you say the humidity that we are experiencing now is coming from high ocean temperatures, that are warmer than usual? ALEX TARDY: Across the globe, if you look at all of the ocean temperatures in the globe, they are ranked number one for the warmest on record. Even if you look locally in the Baja California area, our waters are much above normal as well. Some of that is attributed to recent developments with El NiÒo, but not all of it is related. We're talking local and global water temperatures. MAUREEN CAVANAUGH: The high ocean temperatures made many forecasters predict a strong El NiÒo coming to California this fall. Is that wishful thinking? ALEXANDER GERSHUNOV: I think so. The conditions that give us predictably with winters have to do with very strong El NiÒo. The way the El NiÒo was developing three months ago, it was checking the strongest El NiÒo we were having in 1997 and 1998. People have been predicting a similar magnitude of El NiÒo, but since then it has petered out. We are looking at a mediocre El NiÒo event, which we can't really hang a very good forecast on. MAUREEN CAVANAUGH: So you're still predicting El NiÒo? ALEX TARDY: Our computer modeling that is run every day and several times a month, it is indicating that would at least get into a weak state of El NiÒo. The problem is, historically even moderate to weak El NiÒo's have had extreme variability of precipitation in California. Some are dry. 1976 and 1977 were the start of the worst droughts, the drought that we're comparing our current drought to. There's not much correlation between weak to moderate El NiÒo's for above normal precipitation, in southern California or anywhere in California. MAUREEN CAVANAUGH: If our drought continues another year, let's say the worst-case scenario, and we don't get much pain out of this El NiÒo. Will that put us historically? Will this be one of the driest stretches for San Diego California? ALEX TARDY: We have to look at it as a whole in San Diego, because that affects our water supply and fire conditions California. Right now we're behind the 1976 and 1977 droughts in terms of the deficit of precipitation, the stress on fire weather conditions and fuels which feed the fires. If we have a nether dry year, it will put us in first place. Now to get out of the start, we would need not just a normal season statewide, we would need 150% of normal. I know we cannot predict that occurring, because of the weak El NiÒo that is developing. It is expected to develop further in the fall in the winter, but it is a flat line right now. It's not in the state of a strong El NiÒo we could associate with more precipitation. That does not mean that will not get big storms in the winter. It is a long-term production. We need several significant storm to make it different. MAUREEN CAVANAUGH: Didn't this look like it was going to be a really big El NiÒo? Wasn't the ocean temperature as high as when we did have really big El NiÒo back in the 90s? ALEXANDER GERSHUNOV: It started out like the big El NiÒo we had in the 90s, since then it has petered out. We're still looking at El NiÒo, but nothing special. The problem is, in recent history, we only had two really big El NiÒo's. They both brought a lot of precipitation to the region, but two of them is not a example in statistics in climatology. Every El NiÒo develops in its own way, each one is different. They follow their own roadmap. We don't have enough big events to know how each one of them develops. Just two of them in the recent history, this one is very different from those. MAUREEN CAVANAUGH: It's not enough to go on? ALEXANDER GERSHUNOV: It's not working out to be a big one at this point. MAUREEN CAVANAUGH: We did actually get some rain as you pointed out earlier. Are these just thunderstorms that go astray? ALEX TARDY: It's difficult to associate getting rain. My kids joked and said dad, that the drought must be over with. We're looking at a three-year deficit of precipitation, three years statewide since 2010. Nthis is just a drop in the bucket. Most of it is in the desert, and we have had devastating flash flooding, but it is not going to the water supply or soil moisture, and it is not helping the trees and the vegetation which is really dormant right now, as is typical of August. It is not much help. It is nice short-term relief that will help us a little bit to suppress some fire activity that was developed, but for long-term it does not help much at all. MAUREEN CAVANAUGH: Talking about long-term forecasting, what does it tell you the severity of Santa Ana's may develop in the next few months? ALEX TARDY: We have difficulty correlating El NiÒo and La NiÒa with Santa Ana's. We have seen some big Santa Ana events in the El NiÒo years, less frequently but big events. Really the key is, the trees and vegetation are so stressed and so dry that all it will take is one. We know that we will get one or two, we always get one or two Santa Ana wind events. This year was unusual, seeing two big ones in May. It's not that we don't see them in May, but it's the magnitude. Those were November, October events in May. We'll be holding our breath. We'll get Santa Ana's but it's hard to say how many. ALEXANDER GERSHUNOV: I agree, there is no way to predict Santa Ana season with El NiÒo. But the one thing I would add, the peak of Santa Ana season is actually in December, and that coincides closely with the week of our raining season. If we get another dry year, it is likely that fuels are going to stay dry into the winter, which is the peak of the Santa Ana season we get the most frequent Santa Ana events. That means we will have elevated fire danger in the middle of winter, when it is typically wet. MAUREEN CAVANAUGH: I hate to end on that note, but I want to thank you both very much.