Updraft: August 17, 2009 Archive

Season's first hurricane churns in Atlantic

Posted at 8:26 AM on August 17, 2009 by Paul Huttner

Hurricane Bill takes shape today in the Atlantic Ocean.

It took a while this year, but the Atlantic hurricane season is finally underway.

Hurricane Bill became the season's first hurricane today. Bill is still over a thousand miles east of the Lesser Antilles, but it may become a major hurricane by Wednesday. The NHC forecast ramps Bill's winds up to around 115mph making it a category 3 storm.

The official NHC track takes Bill in the general direction of Bermuda in 5 days. That would be good news for the U.S. as that track usually keeps hurricanes east of the U.S. coastline.

T.D. Ana briefly reached tropical storm strength over the weekend to become the season's first named storm. Conditions appear unfavorable for Ana to return to tropical storm strength.

Claudette flared rapidly Sunday in the Gulf of Mexico to become the season's third named storm. Warm Gulf waters quickly fueled Claudette to a tropical storm with 50 mph winds. Claudette made landfall early Monday in the Florida Panhandle. It is fortunate that Claudette ran out of real estate in the Gulf of Mexico or it may have reached hurricane strength if it was over water for another 24 hours.

Bill's development to hurricane strength on August 17th is a fairly late start to the season. According to the NHC, the latest start dating back to 1851 was on October 8th in 1905. Since 1966 when weather satellites began routine hurricane monitoring the latest first hurricane of the season was on September 11th, 2002 when Gustav formed.

It will be interesting to watch Bill's progress this week in the Atlantic.

Stay tuned.

PH

Unusual "heat burst" hits Pierre, SD

Posted at 4:00 PM on August 17, 2009 by Paul Huttner (1 Comments)

Here's one you can file under "weird weather news."

Early Friday morning around 2 am, the temperature in Pierre, South Dakota rose from 79 to nearly 90 degrees. That's right; the temperature rose about 11 degrees in an hour, in the middle of the night!

What caused this unusual rise?

It's called a heat burst. It can happen when thunderstorms die out.

Here's what likely happened in the skies over Pierre Friday.

The updrafts that have built the storms are gone. The air and water that has been lifted high into the atmosphere now begins to descend toward the ground. At first there may be some evaporational cooling of the air mass. This makes the air heavier and it descends more rapidly.

As the air dries and speeds up, it begins to warm as it descends. Descending air can warm at 5 to 10 degrees per thousand feet of descent depending on conditions. This is similar to a Chinook Wind effect in the lee of the Rockies.

As the downdraft hit the ground in Pierre, the winds kicked up and temperatures shot up to 90 degrees at 2 in the morning!

Heat bursts are almost impossible to detect and forecast. There is really no good way to measure what's coming at you from 10,000 feet straight above you in the middle of the night.

It's amazing how many cool weather phenomena nature can send our way. It certainly keeps my life interesting!

PH

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