Warmer Than Usual Ocean Temperatures in Northeast Mean Heavier Rain From Hurricane Sandy

land and ocean temperature anomalies september 2012 map NOAA/Public Domain

The I'm-not-calling-it-a-friggin-Frankenstorm (aka Hurricane Sandy) is by all accounts, from the near hysteric mainstream media to the more sober yet appropriately serious, concerned (and usually more accurate than everyone else) folks at Weather Underground, a big deal, with potential devastating rain, wind, and high storm surges made worse by the coincidence with the full moon.

We're talking potentially another billion dollar natural disaster here, if Sandy tracks over the mid-Atlantic states, rather than the Northeast. Be prepared, pay attention, keep calm, carry on and all the rest of it.

All that said, with all the talk about the conditions combining to make this such an unusual storm, there's one thing that really caught my eye, yet hasn't been reported ad nauseum yet: Higher than normal ocean temperatures in the Northeast, may make all of this worse.

Here's what Dr Jeff Masters wrote yesterday (the emphasis is mine):

If Sandy makes landfall farther to the north near Maine and Nova Scotia, heavy rains will be the main threat, since the cold waters will weaken the storm significantly before landfall. The trees have fewer leaves farther to the north, which will reduce the amount of tree damage and power failures compared to a more southerly track. However, given that ocean temperatures along the Northeast U.S. coast are about 5°F above average, there will be an unusually large amount of water vapor available to make heavy rain. If the trough of low pressure approaching the East Coast taps into the large reservoir of cold air over Canada and pulls down a significant amount of Arctic air, the potential exists for the unusually moist air from Sandy to collide with this cold air from Canada and unleash the heaviest October rains ever recorded in the Northeast U.S., Nova Scotia, and New Brunswick. This Northeast U.S. scenario would probably cause damages near $100 million dollars.

In case you need reminding, these higher than normal ocean temperatures fit solidly into the broader global trend towards warmer temperatures—though regionally they are much greater than the global average (as the chart at top shows, with the red areas being up to 5°C above normal). Globally, average ocean temperature was 0.99°F above the 20th century average for September, according to NOAA stats—making it the second warmest September for ocean temperatures on record, tying with 1997.

As for the part about a large amount of water vapor being available, this too is part and parcel with global warming—and is in fact an often overlooked factor in the type of extreme weather and changes that become more likely as the planet as a whole warms.

Warmer Than Usual Ocean Temperatures in Northeast Mean Heavier Rain From Hurricane Sandy
Ocean temperatures in the Northeast are 5°F above normal, following the second warmest average ocean temperatures ever recorded for September.

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