End in sight for Nadine; 96L no threat to land

Never-ending Tropical Storm Nadine hit its peak intensity of 90 mph on Sunday afternoon, but is now steadily weakening as it encounters cool 22 - 23°C waters. Nadine is responsible for these cool waters, as the storm passed over the same location earlier in its life and mixed the cool waters to the surface. Nadine will have accumulated 19 days as a tropical cyclone later today, but the end is in sight. Nadine will be over waters no warmer than 24°C this week, and wind shear will increase to 30 knots by Wednesday. The HWRF model shows Nadine dissipating on Thursday as it moves through the Azores Islands; the ECMWF model predicts that Nadine will pass through the Azores on Thursday as a minimum-strength tropical storm with 40 mph winds, then dissipate on Friday. If Nadine lasts until Wednesday evening, it will become one of the five longest-lived Atlantic tropical cyclones of all-time. Tropical cyclones include tropical depressions, tropical storms, and hurricanes, but not extratropical storms; I am counting Nadine's 24-hour stint as a subtropical storm as it being a tropical cyclone.) According to the official HURDAT Atlantic database, which goes back to 1851, only five 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) 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 1. MODIS satellite image of Hurricane Nadine taken at 11:53 am EDT Sunday, September 30, 2012. At the time, Nadine was at peak strength, with top winds of 90 mph. Image credit: Navy Research Lab, Monterey.

96L off the coast of Africa no threat to land
A tropical wave that emerged off the coast of Africa over the weekend (Invest 96L) has a moderate amount of spin and a small area of disorganized heavy thunderstorms. The storm is located about 500 miles southwest of the Cape Verde Islands, and is headed west-northwest at 10 - 15 mph. Wind shear is a moderate 10 knots, and is predicted to remain light to moderate, 5 - 15 knots, through Friday. The atmosphere surrounding 96L is fairly moist, and the disturbance does have a good degree of model support for becoming a tropical depression by late in the week. In their 8 am EDT Tropical Weather Outlook, NHC gave 96L a 30% chance of becoming a tropical depression by Wednesday morning. 96L is likely to get pulled northwards by a large trough of low pressure over the Central Atlantic late this week, and should not be a threat to the Lesser Antilles Islands.

Jeff Masters