30 March, 2017

2017-18 ENSO Watch: Pacific, Indian Ocean SST Anomalies Greatly Resemble 1877

In case anyone hasn't already noticed, yes, California has gotten plenty of help this past winter as far as drought relief is concerned. OC, Ventura, and Santa Barbara counties have gone from exceptional drought down to moderate drought during the 2016-17 water year, and in the rest of the state, there is nothing left of the drought at all. However, we are still not completely out of it. That said, if the oceans are any indication, we may well be.

While the flooding rains in California have just about ended for the 2016-17 water year, the same cannot be said about the devastating floods in Peru. What has been forming in the Atlantic and eastern Pacific is a south-based (warm south, cold north) SST dipole, which has allowed the ITCZ to intensify far to the south of its normal position — about 10 degrees south of the equator in the Eastern Pacific in particular, and the result has been an Atlantic that is more or less stuck in winter mode even as we enter spring. The result, in turn, has resulted in strong northerly winds off Peru that have kept the coastal region warm, and, as a result, have kept the air wet. Moreover, strong negative WPO has supercooled the western Pacific, and, to boot, the extreme northeastern Pacific, despite having cooled considerably in March, is now warming up again very rapidly.

In addition, there has been a lot of cooling of the eastern Indian Ocean, and of the West Australian Current in particular, that has been more or less coupled with a warming of the southwestern Indian Ocean between Madagascar and South Africa. This is a precursor to a positive Indian Ocean Dipole, which is capable of helping a developing El Niño event out. Also, a cold Baja California anomaly is coupled with a warm anomaly further north — a high-over-low dipole that favors a Southern Hemisphere Booster response.

Sea surface temperature anomalies at 12:00 UTC on Thursday, March 30, 2017. Note strong positive IOD trying to form, along with rapidly cooling tropical Atlantic.

A similar map, but this time a monthly average of the sea surface temperature anomalies from March 1877. Note the presence of the SW Pacific (near NZ) warm blob, not to mention the same SE Indian Ocean cold pool and the same anomalously cold NW Pacific. This is almost identical to the current situation.

What followed the 1877 precursor was something for the record books to say the least: an El Niño event so powerful that 1997-98 and even, if Modoki events are counted, 2015-16 were put to shame by it. Are we in for a repeat? It remains to be seen, but the odds are indeed high.