2009

After a very active start to the normally meteorologically quiescent month of June, we have now entered a more typical summer regime. Temperatures across the state are relatively cool at the moment, but these are expected to trend towards or even a little above seasonal normals by later this week. The models are currently indicating a small possibility that a weak cutoff low near the SoCal coast will draw a bit of moisture northward from Tropical Storm Andres, but this looks somewhat unlikely at the moment. If the situation changes and a larger volume of moisture is advected into the southerly flow aloft, I will update later this week.

More interesting and certainly more important in the long term is the evolving ENSO event in the Pacific. SST warming has been significant in the past few weeks and positive anomalies are now well-established in all Nino regions. In fact, average anomalies are now around 0.7  degrees C basin-wide. Should the present anomalies persist for the next two months, we would officially have a weak El Nino on our hands by August. All indications, however, are that the warming of the tropical East Pacific will continue, and that anomalies wil continue to increase with time. Dynamical climate models are unanimous in predicting El Nino conditions for the coming fall and winter, and even the statistical models have now come into line. This is very early to be experiencing significant El Nino-related warming of the sea surface, which may be an indication of the eventual magnitude of the event. There does appear to be some correlation between early onset of El Nino and moderate to strong events. Additionally, the frequency of strong El Nino events appears to be 10-15 years (though this is determined by a relatively small sample size–4 events between 1960 and 2009). Since the last major El Nino was 12 years ago, we do appear to be statistically “due” for another. The next 2-3 weeks will be interesting, and it will be informative to watch the SST anomaly maps and dynamical model forecasts. Right now, I would say that there is a near-certainty that a weak El Nino event will develop by September and a very strong possibility that it will continue to strengthen to a moderate event by October. What happens beyond the fall is uncertain, but there is a real possibility (probably less than 50%, but this is still a large number) that El Nino will continue to strengthen and become strong by the beginning or middle of next winter. Should this occur, there would likely be significant implications for the state of CA.  Even if the event peaks in the moderate category, I would expect some impacts to be felt at least in SoCal. A quick glance at strong SST anomalies right off the CA coast and a recollection of the recent anomalous weather events in CA may indicate that an El Nino-type circulation pattern already exists and has been influencing CA weather. In any case, I will be updating on the ENSO scenario occasionally through the summer and into the fall. Stay tuned…and the Seasonal Outlook will  be updated after the new weekly SST maps come out on Wednesday.