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Sandy forms south of Jamaica; TD 19 forms in middle Atlantic

By: Dr. Jeff Masters, 9:48 PM GMT on October 22, 2012

The Hurricane Hunters found a band of 40 mph winds on the southeast side of Tropical Depression Eighteen this afternoon, prompting NHC to upgrade the system to Tropical Storm Sandy. Sandy is over very warm waters of 29.5°C, is in a moist environment, and has light wind shear of 5 - 10 knots. These conditions are very favorable for intensification, and Sandy's heavy thunderstorms are steadily organizing into curved spiral bands, as seen on satellite loops.

Figure 1. Late afternoon satellite image of Tropical Storm Sandy.

Forecast for Sandy
Wind shear is forecast to be in the low to moderate range, 5 - 20 knots, through Wednesday afternoon. This should allow continued development of Sandy, and rapid development is possible. The latest SHIPS model forecast is calling for a 52% chance that Sandy's winds will increase by 30 mph over a 24-hour period. The 5 pm EDT NHC Wind Probability Forecast gave a 25% chance that Sandy will be a hurricane by 2 pm EDT Wednesday, when the center should be close to Jamaica. Wind shear will rise to a high 25 - 30 knots by Thursday, which should weaken Sandy. By Friday, Sandy should be in the Central or Eastern Bahamas, and wind shear may increase further, making Sandy more of a hybrid subtropical storm. It is unclear at this point whether or not the trough pulling Sandy to the north will be strong enough to pull the storm all the way out to sea to the northeast; a very complicated steering environment will develop late this week, and it is possible that a narrow ridge of high pressure could build in over Sandy, and force the storm to the northwest, with a potential threat to the Northwestern Bahamas and U.S. East Coast by Saturday, as predicted by the ECMWF model. Sandy is not a threat to be a hurricane at that time, due to very high wind shear. Heavy rains are the main threat from Sandy.

Sandy's place in history
Sandy is the eighteenth named storm of the 2012 Atlantic hurricane season, tying this year with 1969 for seventh busiest Atlantic season since record keeping began in 1851. Here are the busiest Atlantic hurricane seasons on record:

2005 (28 named storms)
1933 (20 named storms, according to a new re-analysis)
1887 (19 named storms)
2010 (19 named storms)
2011 (19 named storms)
1995 (19 named storms)
1969 (18 named storms)
2012 (18 named storms)

There are two weak and short-lived storms from 2012 that stayed far out sea, and would likely have gone unnoticed in the pre-satellite era (before 1960): Tropical Storm Joyce and Tropical Storm Oscar. And while this season has been very busy for total number of named storms, we've had a below-average number of major hurricanes (just Hurricane Michael), and the total destructive power of the 2012 hurricane season as measured by the Accumulated Cyclone Energy (ACE) is only about 20% above average. See our newly-launched Accumulated Cyclone Energy (ACE) page for a storm-by-storm breakdown of this years ACE, plus historical ACE stats for each ocean basin. Thanks go to Angela Fritz for putting this together!

Figure 2. MODIS satellite image of TD 19 taken at 12:30 pm EDT October 22, 2012. Image credit: Navy Research Lab, Monterey.

Tropical Depression Nineteen forms in the middle Atlantic
Tropical Depression Nineteen is here, and appears poised to become Tropical Storm Tony by early Tuesday morning. TD 19 has a modest area of heavy thunderstorms, as seen on visible satellite images, and dry air from the upper-level low pressure system that it formed underneath is slowing development. TD 19 is over warm waters of 28°C, and wind shear is a moderate 10 - 20 knots. This shear is forecast to remain in the moderate range until Wednesday morning, which should allow TD 19 to develop into Tropical Storm Tony over the next day. On Wednesday, TD 19 is expected to encounter high wind shear of 20 - 30 knots, which should prevent further strengthening. TD 19 will not threaten any land areas, and is unlikely to reach hurricane strength.

Jeff Masters


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