A wild and wacky week in the tropics could get even weirder

It’s been a wild and weird start to 2016 across the tropics. And the weird could get even weirder next week.

First let’s rewind to New Year’s Eve 2015, when a short lived tropical depression bubbled up in the central Pacific only about 200 miles from the equator. This is unusual — not that a tropical cyclone formed in December (this happens about once every five years on our side of the world), but that a tropical depression formed this close to the equator. In fact, fewer than one percent of all tropical cyclones form at this low of a latitude.

Tropical Depression Nine moved even closer to the equator on New Year’s Day, becoming the lowest latitude tropical cyclone on record in the western hemisphere at 2.2 degrees north. What’s even more amazing was the initial disturbance that became Tropical Depression Nine was at one point spinning counter-clockwise in the southern hemisphere very close to the equator (for the not-as-weather-savvy reader, large, long-lived low pressure systems in the southern hemisphere are supposed to spin clockwise):

Satellite loop of the disturbance that later became Tropical Depression Nine. Notice the counter-clockwise spin to the south of the equator. Loop via Dan Lindsey/NOAA.

While this is certainly rare it isn’t unprecedented. The low pressure system that later became Cyclone Agni in 2004 performed a similar feat, acquiring counter-clockwise spin north of the equator but keeping its counter-clockwise rotation while it briefly dipped south of the equator. This can only happen for large, long-lived low pressure systems very close to the equator where the background spin of Earth (the Coriolis force) is small or nonexistent. In this case the spin from the northern hemisphere was briefly taken south of the equator and maintained by forces in the atmosphere other than Coriolis (a balance that meteorologists call cyclostrophic balance).

And if that wasn’t enough, on Tuesday the Brazilian Navy was monitoring a Subtropical Depression in the South Atlantic in a part of the world where fewer than a handful of tropical cyclones have ever formed.

Weather map for Tuesday, January 5th, 2016, at 1200 UTC from the Brazilian Navy Hydrographic Center. Note the newly designated Subtropical Depression off the coast of Brazil.

Although the subtropical system wasn’t able to muster up enough tropical warmth to become a full fledged tropical cyclone, it certainly raised eyebrows for a period of time.

Fast forward to yesterday, and yet another tropical oddity happened only a few hundred miles from where Tropical Depression Nine formed last week. Tropical Storm Pali (previously Invest 90-C in my tweet above) became the earliest named storm on record to form in the central Pacific and, although it poses no threat to land, is a healthy storm only a few ticks away from hurricane status.

And to top off this wild and wacky week in the tropics, the National Hurricane Center in Miami is monitoring a potent non-tropical low pressure system near Bermuda for possible subtropical or even tropical development. In the Atlantic. In January.

Like some of our other oddities, tropical development in the Atlantic in January would be rare but not unprecedented. It’s happened five times that we know of, most recently in January of 2006 when Tropical Storm Zeta (which technically formed in December of 2005) lingered into the new year. The strongest January Atlantic storm was an unnamed hurricane in 1938.

Though this current low pressure system is moving away from the United States and poses no direct threat here (other than some increased east coast swell), it will bring heavy rains and blustery 60-plus mph wind gusts to Bermuda today into early tomorrow. If the low pressure system acquires subtropical or tropical characteristics over the Atlantic it would be named Alex, the first named storm of 2016.

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