Subtle changes in the waters of the eastern equatorial Pacific can have outsized impacts on global weather patterns on a year-to-year basis.
A slight warming or cooling here – like running a fever – can throw global circulations off-kilter.
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Everything from rain and temperature patterns to sea levels off the east coast can see dramatic fluctuations when eastern Pacific waters warm or cool by as little as half a degree Celsius (about a degree Fahrenheit).
Most importantly for us, tropical activity is regulated by warm episodes – called El Niño – and cool episodes – called La Niña.
Since last fall, the Pacific has experienced a severe and extended cooling, or La Niña, episode.
In many ways, the impacts have looked very typical. The hot and dry conditions across Texas and the southern Plains this year, for example, can be attributed to changes in the jet stream pattern from La Niña.
In the tropics, though, the traditional look of a La Niña atmosphere hasn’t yet taken shape.
During La Niña episodes, the eastern Pacific hurricane season is usually softened by more hostile conditions.
So far this year, though, the season is off to one of its most active starts on record, with already five hurricanes, something we don’t typically see until the end of August.
Meanwhile in the Atlantic, hostile wind shear across the bellwether Caribbean Sea – typically reduced during La Niña years – has been running well above average to begin July and above the lower values we’ve seen with other historic La Niñas.
While these developments are surprising, it’s still early in the season to discern long-term implications.
With La Niña in the process of recharging, we’d expect to see more conducive conditions for tropical development headed into the peak months, which is why seasonal hurricane forecasts in the Atlantic remain historically high.
This week should stay mostly quiet in the tropics, but, as we discussed in yesterday’s newsletter, the Atlantic looks to transition to a more favorable regime for storminess as we round out July next week.
Estelle in the eastern Pacific, originally forecast to strengthen into a Category 3 hurricane this week, has leveled off as a Category 1 storm, and is no longer expected to strengthen much further as is churns over open waters.