By Dr. Jeff Masters

Published: 4:12 PM GMT on October 03, 2012

The first new tropical depression in the Atlantic since September 11 is here, Tropical Depression Fifteen. TD 15 is destined for a short life, though, and will not be a threat to any land areas. The storm is already showing signs that moderate wind shear of 10 – 20 knots is interfering with development, with most of the storm’s heavy thunderstorms displaced away from the center of circulation. Wind shear is expected to rise to the high range, above 20 knots, on Thursday and Friday as the storm turns north and then northeast. Ocean temperatures will cool from 28°C today to 25°C by Saturday, and all of the computer models show TD 15 ceasing to exist by Saturday, as the storm becomes absorbed by a large extratropical storm. TD 15 is a classic example of a weak, short-lived tropical cyclone that would have gotten missed before satellites came around. If TD 15 strengthens, it will be called Tropical Storm Oscar.

Figure 1. MODIS satellite image of TD 15 taken at 8:52 am EDT Wednesday, October 3, 2012. At the time, TD 15 was just forming and had top winds of 35 mph. Image credit: Navy Research Lab, Monterey.

Nadine touring the Azores Islands–again
I’m-not-dead-yet Tropical Storm Nadine is back for a second tour of the Azores Islands, where tropical storm warnings are up for the storm’s expected arrival tonight. Nadine is struggling with cool 21 – 22°C waters and high wind shear of 20 – 30 knots, and could transition to an extratropical storm later today or on Thursday as it heads east at 14 mph. Nadine is up to 21 days as a tropical or subtropical cyclone as of 2 pm today, making it the fifth longest-lived Atlantic tropical cyclone of all-time (tropical cyclones include tropical depressions, tropical storms, and hurricanes, but not extratropical storms.) According to the official HURDAT Atlantic database, which goes back to 1851, only five previous Atlantic tropical cyclones have lasted 21 days or longer (thanks go to Brian McNoldy for these stats):

1) San Ciriaco Hurricane of 1899: 28 days
2) Ginger, 1971: 27.25 days
3) Inga, 1969: 24.75 days
4) Kyle, 2002: 22 days
5) Nadine, 2012: 21 days
5) Hurricane Four, 1926: 21 days

According to the Hurricane FAQ, the all-time world record is held by Hurricane John in the Eastern Pacific, which lasted 31 days as it traveled both the Northeast and Northwest Pacific basins during August and September 1994. (It formed in the Northeast Pacific, reached hurricane force there, moved across the dateline and was renamed Typhoon John, and then finally recurved back across the dateline and renamed Hurricane John again.) Of course, there may have been some longer-lived storms prior to 1961 that we didn’t observe, due to the lack of satellite data.

Figure 2. MODIS satellite image of Hurricane Nadine taken at 8:45 am EDT Wednesday, October 3, 2012. At the time, Nadine had top winds of 50 mph. Image credit: NASA.

Jeff Masters

from:    http://www.wunderground.com/blog/JeffMasters/article.html?entrynum=2248