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Irene and TD 10

By: Dr. Jeff Masters, 8:17 PM GMT on August 12, 2005

Hello all, I'm back after a long vacation to Yellowstone--a great place to tune into nature and forget the hassles of civilization and your job and just live day-to-day in appreciation of the amazing beauty of a truly extraordinary place. I'll upload a few of my photos and share some reflections of my Yellowstone trip this weekend. It was great to forget about the tropics for a while, but I'm happy to be back to daily blogging as we enter the peak two-month stretch of what has been an already very long hurricane season.

Irene is almost a hurricane. The deep convection at the center of Irene has increased markedly the past few hours, and the first Hurricane Hunter mission into the storm at 2:15pm EDT found an 8 nm wide center with central pressure of 997 mb, and peak surface winds of 70 mph. Irene is over warm 29 - 30C waters, is in a low shear environment, and has good upper-level outflow in all quadrants except the southeast. Irene is sucking in some dry mid-level air from the southeast, which is inhibiting her development some. She is moving to the northwest, which will soon put her in an area of cooler sea surface temperatures (SSTs), left behind by Franklin and Harvey when they churned up these same waters earlier this month. These cooler SSTs should act to keep Irene from rapid intensification, and I expect she will attain Category 1 hurricane status but intensify no further the next two days. Once Irene moves closer to the U.S. coast, there is a narrow area of warmer SSTs along the Gulf Stream that may help intensify her, though. I won't speculate on Irene's track at this point, since steering currents will become weak and Irene may enter a period of erratic motion by Sunday. I'd estimate the chances of Irene getting her name retired by becoming a major hurricane and hitting the U.S. at about 5%. It's pretty rare for a storm this far north to develop into a major hurricane and hit the U.S. Too many things can go wrong--the storm can hit cool SSTs, experience high wind shear, or get recurved out to sea by a fast-moving trough.

Figure 1. Irene's motion to the northwest will soon put her in an area of cooler SSTs left behind by Franklin and Harvey. However, the tropical disturbance at 12N 43W was plenty of warm water in front of it as it moves WNW at 10-15 mph. Image credit: U.S. Navy.

TD 10?
The system that might have a greater chance of developing into a serious threat lies in the middle tropical Atlantic near 12N 43W. A closed low pressure with central pressure of 1012 mb has developed here from a tropical wave, and although convection has declined a bit this afternoon, this system has an excellent chance of becoming TD 10 this weekend. Buoys in the vicinity already report winds of 20-25 knots, and the low lies in an area of light wind shear and warm waters (28 - 29C), with plenty of warm water in front of it as it moves WNW at 10-15 mph. The low is far enough south to avoid entraining in some dry Saharan air that lies to the north.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.