La Nina taking hold
The Pacific is cooling off, and that may be ominous.
In its weekly update , the government's Climate Prediction Center is saying that a La Nina cooling event is "developing" in the equatorial Pacific and it's looking more as though La Nina is going to rule.
The Pacific long since has exited the state of El Nino, an anomalous warming. Sea surface temperatures in the key El Nino-La Nina tracking region warmed significantly in the fall and reached a peak at the end of the year when they were about 2.5 degrees Fahrenheit above normal.
They have fallen steadily since April, and for the last month have averaged about 1.3 degrees below normal. That's low enough to qualify as a La Nina state, but to qualify as a full-fledged La Nina the cooling would have to persist into January.
Statistically, hurricane activity is brisker in La Nina year than it is during El Nino, when the warming generates strong west-to-east shearing winds that can blow out potential hurricanes before they have a chance to mature.
When El Nino isn't present, the shearing winds aren't as strong. With La Nina, they are virtually non-existent.
The state of the Equatorial Pacific isn't the only factor affecting hurricanes. The 1969 season was an active one, despite a weak El Nino. The 1956 season was not particularly active, despite La Nina.
But hurricane forecasters have been steadfast in warning that this is going to be a nasty season. One thing they are looking at is the warm Atlantic, which also tends to favor busy seasons.
Right now the tropical and subtropical Atlantic and the waters off the U.S. East Coast are quite warm, ranging from 1 to 3 degrees above normal.
Embedded in the CPC La Nina update you can find a tidy map showing the aforementioned ocean temperatures.
Also, take a look at the 90-day temperature map. The entire East has been above normal; the West, the mirror opposite. That has something to do with the changing regime in the Pacific.