This is our first heads-up of the season. Although we are 83 days into it, the season is still around three weeks from the statistical peak. From NOAA....
...From Unisys the Sea Surface Temperature anomaly map:
The extreme anomaly we saw along the US eastern seaboard in May has dissipated a bit but is still running above the 30-year average.
Meaning storms that get to, say South Carolina, will have fuel to intensify.
Probably more interesting is the west coast of South America at the equator and extending out to the Dateline: that damn near looks to be a budding La Niña....
We followed that with September 15's "NOAA Climate Prediction Center: 'ENSO Alert System Status: La Niña Watch'"
And here's the reason it's important, from NOAA's Climate.gov:
Impacts of El Niño and La Niña on the hurricane season
With the approach of the 2014 hurricane season and the strong potential for El Niño to develop during the next few months, the effect that El Niño has on both the Atlantic and Pacific hurricanes seasons is worth exploring. The hurricane impacts of El Niño and its counterpart La Niña are like a see-saw between the Pacific and Atlantic oceans, strengthening hurricane activity in one region while weakening it in the other.
Typical
influence of El Niño on Pacific and Atlantic seasonal hurricane
activity. Map by NOAA Climate.gov, based on originals by Gerry Bell.
Simply put, El Niño favors stronger hurricane activity in the central and eastern Pacific basins, and suppresses it in the Atlantic basin (Figure 1). Conversely, La Niña suppresses hurricane activity in the central and eastern Pacific basins, and enhances it in the Atlantic basin (Figure 2).
Typical
influence of La Niña on Pacific and Atlantic seasonal hurricane
activity. Map by NOAA Climate.gov, based on originals by Gerry Bell.
These impacts are primarily caused by changes in the vertical wind shear, which refers to the change in wind speed and direction between roughly 5,000-35,000 ft. above the ground. Strong vertical wind shear can rip a developing hurricane apart, or even prevent it from forming.And wind speed?
ENSO perturbs tropical and subtropical atmospheric circulation
During El Niño, the area of tropical Pacific convection and its associated Hadley circulation expand eastward from the western Pacific, sometimes extending to the west coast of South America. (A tutorial on El Niño and La Niña can be found at the NOAA Climate Prediction Center website.) At the same time, the equatorial Walker circulation is weaker than average.
These conditions produce an anomalous upper-level, ridge-trough pattern in the subtropics, with an amplified ridge over the subtropical Pacific in the area north of the enhanced convection, and a downstream trough over the Caribbean Sea and western tropical Atlantic. Over the central and eastern Pacific, the enhanced subtropical ridge is associated with weaker upper-level winds and reduced vertical wind shear, which favors more hurricane activity.
Over the Atlantic basin, the amplified trough is associated with stronger upper-level westerly winds and stronger lower-level easterly trade winds, both of which increase the vertical wind shear and suppress hurricane activity. In addition to enhanced vertical wind shear, El Niño suppresses Atlantic hurricane activity by increasing the amount of sinking motion and increasing the atmospheric stability.
La Niña has opposite impacts across the Pacific and Atlantic basins. During La Niña, the area of tropical convection and its Hadley circulation is retracted westward to the western Pacific and Indonesia, and the equatorial Walker circulation is enhanced. Convection is typically absent across the eastern half of the equatorial Pacific.
In the upper atmosphere, these conditions produce an amplified trough over the subtropical Pacific in the area north of the suppressed convection, and a downstream ridge over the Caribbean Sea and western tropical Atlantic. Over the central and eastern subtropical Pacific, the enhanced trough is associated with stronger upper-level winds and stronger vertical wind shear, which suppress hurricane activity. Over the Atlantic basin, the anomalous upper-level ridge is associated with weaker upper- and lower- level winds, both of which reduce the vertical wind shear and increased hurricane activity. La Niña also favors increased Atlantic hurricane activity by decreasing the amount of sinking motion and decreasing the atmospheric stability....MORE
These long haul Cape Verde storms coming off the Sahara would have been torn apart in prior seasons of the last decade or not even formed if, as was the case for quite a chunk of the "twenty-teens" the wind had been laden with sand/dust in the very dry Saharan Air Layer.
The fact the disturbances are not ripped to shreds by wind shear means they have more time to develop.
Look at the Unisys Sea Surface Temperature anomaly map again. The SST anomalies are not exceptionally warm - compared to the 30 year average - from the coast of Africa, the Main Development Region, until you get inside the Leeward Islands and south of Hispaniola but the lack of wind shear means disturbances heading west across the Atlantic have the opportunity to develop into tropical depressions, then into tropical storms and then into hurricanes.
And then, if they are already full blown storms to start with, hitting the warmer waters with their terajoules of energy they can explode. The atomic bomb exploded on Hiroshima was around 63 terajoules so a storm like Harvey (not a Cape Verde, rather a Golfo de México ) which was moving the equivalent of a million Hiroshima nukes worth of energy per day from the 86°F Gulf water would more accurately be measured in exajoules (1018 [one quintillion] joules) and Irma was moving even more energy, but it's at this point I start to get confused so we'll stop now.
There are dozens of La Niña posts on the blog, use the 'Search blog' box if interested.
The search box is a Google product which distinguishes between "n" and tilde "ñ".
If you go tilde-less you only get results where someone forgot their Spanish. Ahem.
To make a lowercase ñ in Microsoft Windows, hold down the Alt key and type the number 164 or 0241 on the numeric keypad (with Num Lock turned on). To make an uppercase Ñ, press Alt-165 or Alt-0209. Character Map in Windows identifies the letter as “Latin Small/Capital Letter N With Tilde”.
