Fred fading; halfway point of hurricane season reached

By: Dr. Jeff Masters , 1:40 PM GMT on September 10, 2009

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Hurricane Fred peaked in intensity yesterday afternoon, attaining Category 3 strength with 120 mph winds. It is quite unusual to have such a powerful system so far east in the Atlantic, and Fred is only the third major hurricane to exist east of 35W. Fred is also the strongest hurricane so far south and east in the data record. However, this type of system would have been difficult to document before satellite pictures began in the 1960s.

Fred's glory is past, and the storm is on a downslide now, thanks to moderate wind shear of 15 - 20 knots and dry air eating into the hurricane's southwest side. The shear and the dry air will increase over the next few days, with the shear rising above 40 knots by Monday morning. Sea surface temperatures (SSTs) will also cool to near the 26.5°C threshold needed to sustain a tropical cyclone. The combination of high shear, dry air, and cool SSTs will likely kill Fred by Tuesday.


Figure 1. Hurricane Fred at peak strength, 8:55am EDT UTC 9/9/09. At the time, Fred was a Category 3 hurricane with 120 mph winds. Image credit: NASA.

Elsewhere in the tropics
An upper-level low pressure system has moved over Texas and is expected to spawn a surface low pressure system along the Texas Gulf of Mexico coast on Friday. This low will probably have characteristics of both a tropical and extratropical storm. The surface low is likely to move northeastward and move ashore near the Texas/Louisiana border region on Saturday or Sunday. There will be some high wind shear to the west of the low (shear is currently a high 25 knots), so it is uncertain whether this low will be capable of developing into a tropical cyclone. Regardless, this storm will bring heavy rain capable of causing flooding--and help alleviate the exceptional drought conditions over Southeast Texas.

Early next week, we should be alert for tropical storm development over the waters between the Bahamas and North Carolina, along an old frontal zone. None of the reliable models are forecasting tropical storm development in this area or in the Gulf of Mexico, though.


Figure 2. The climatological halfway point of the Atlantic hurricane season is today, September 10.

Halfway point of hurricane season
September 10 marks the halfway point of the Atlantic hurricane season. Despite a late start (Tropical Storm Ana did not form until August 15, the latest start to a hurricane season since 1992), our number of storms has been near average. An average Atlantic hurricane season has 5 named storms, 3 hurricanes, and 1 intense hurricane by the midpoint of the season. So far this year, we've had 6 named storms, 2 hurricanes, and 2 intense hurricanes. A better measure of hurricane activity that takes into account their destructive power is the Accumulated Cyclone Energy (ACE) index. ACE for an individual storm is computed by squaring the maximum sustained winds of the storm at each 6-hourly advisory, and summing up over the entire lifetime of the storm. As of 5am EDT this morning, the seasonal ACE tally was 37.5. This number should rise to around 40 by the end of the day, thanks to the presence of Hurricane Fred. Over the period 1950 - 2005, the average ACE index for a half-season was 51, so 2009 ranks about 20% below average for the halfway point of the season. But when compared to the hurricane seasons we've been having since the current active hurricane period began in 1995, this year has been quite inactive. Between 1995 and 2008, the average ACE index for the halfway point of the season was 72. Thus, 2009 is about 45% less active than what we've been accustomed to over the past 14 years.

We've been lucky this year that the steering currents have aligned to keep our two major hurricanes, Bill and Fred, out to sea. What will the rest of the season have in store for us? I'll present an analysis on Friday.

Twenty years ago on this date
On September 10, 1989, the strong tropical wave that had moved off the coast of Africa the previous day acquired an organized circulation at the surface and began building a concentrated area of heavy thunderstorms near its center. A new tropical depression, the 12th of the season, was born. Moving westward at 20 mph, the depression brought strong, gusty winds and heavy rain showers to the Cape Verdes Islands as it passed to the south. Forecasters at the National Hurricane Center predicted that the steadily organizing tropical depression would strengthen into a tropical storm within the next day or two. The next name on the list of Atlantic tropical storm names for 1989: Hugo.


Figure 3. AVHRR visible satellite image of Tropical Depression Twelve taken on September 10, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

Jeff Masters

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1412. JLPR
Quoting Skyepony:
## ANNULAR HURRICANE INDEX (AHI) AL072009 FRED 09/11/09 00 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=2 NFAIL=5 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##
## ANNULAR INDEX RAN NORMALLY


well then definitively not annular =P
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1410. Skyepony (Mod)
## ANNULAR HURRICANE INDEX (AHI) AL072009 FRED 09/11/09 00 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=2 NFAIL=5 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##
## ANNULAR INDEX RAN NORMALLY
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1408. hydrus
Quoting F4PHANTOM:

12 years old and had been through a Hurricane in Port Arthur in 1957 or 58. Had my share of FUN Don't need any more
Some of the old text books don,t mention it, but Carla was HUGE. I have to read up( its been years )since I researched Carla.I know it reached cat-5 status and lumbered in at about 4 and a half knots with several cycloidal loops around Port Lavaca. Wind gusts-175.
Member Since: September 27, 2007 Posts: 1 Comments: 22683
1407. Gumluvr
Quoting TexNowNM:


Gumluvr, you must be in the channel 6 viewing area, too. (Well, I watch it on computer since I live in the desert.)


Yeah, I live North of Beaumont in a little town named Kountze. It is about 30 minutes from Homeless. Where did you live in Texas before you moved??? Believe it or not, Greg is actually trying to do better this year. He really did a poor job last year. I agree, he is usually a big downcaster. Maybe, that is why Cary does the same. :(
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1405. JLPR
Freddy is looking annular lol xD
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Quoting F4PHANTOM:

12 years old and had been through a Hurricane in Port Arthur in 1957 or 58. Had my share of FUN Don't need any more


You must have gone through Audrey which went over that part of Texas in 1957.
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Quoting JLPR:
Freddy is not moving


Freddy is also not looking terribly healthy.
Member Since: August 3, 2008 Posts: 16 Comments: 5891
1400. JLPR
Quoting tornadodude:


yeah, unless he can move out of the way, he is finished


yep whats left of its anticlone is to the south
so that is its only hope but it is very unlikely =]
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Quoting hydrus:
You were in Carla?
Carla had a huge storm surge. Put the hurt on Galveston. The storm actually came ashore 2 hrs south between Port Lavaca and Corpus Christi. And no, I wasn't alive then.
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Quoting Gumluvr:


We have only had light showers today. Most of it has been to the south and over your way. I noticed Greg had up the chances of rain for this weekend.


Gumluvr, you must be in the channel 6 viewing area, too. (Well, I watch it on computer since I live in the desert.)
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i remember last week one of the models showing that fred was going to stall out right around where he is stalling now. i wish i could remember what model that was. someone posted it. does anyone else remember that model? what is going on in the gulf of mexico?
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Quoting JLPR:


shear is trying to remove the convection but Freddy keeps fighting trying to keep its convection
but these 20 to 40kts of shear should do their job soon


yeah, unless he can move out of the way, he is finished
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Link

The punch of dry air coming into the southwest side of the low is characteristic of an occluding extra-tropical cyclone, however the convection is at the moment closer to the center, more characteristic of a tropical or sub-tropical cyclone. Due to its close proximity to the coast and as to not create a fuss in a highly populated area...and the fact that it has more extra-tropical than sub-tropical structure is probably why it isn't (and probably won't be) designated as a sub-tropical storm.

I dub thee Hybrid Gale! :)
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1390. centex
Quoting JLPR:
Freddy is not moving

Yea finished N for now
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1389. hydrus
Quoting F4PHANTOM:

Don't remember the amount of rain from Carla but I do remember seeing pics of flooding where Friendswood is now.
You were in Carla?
Member Since: September 27, 2007 Posts: 1 Comments: 22683
1388. JLPR
Quoting tornadodude:


almost appears to be moving SE....


shear is trying to remove the convection but Freddy keeps fighting trying to keep its convection
but these 20 to 40kts of shear should do their job soon
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Quoting TexNowNM:


Channel 6 definitely plays down storms. No over-hype there. I don't know anything about 12.

Thanks for the update, Homeless.

Just an off-the-wall question. Do any of you remember when Alison was just building up and Cary Cooper kept saying about it, "I'm not impressed." The newscaster kept asking, "Shouldn't we be worried?" "Could this be a problem?" and he just kept saying how unimpressed he was?


lol. I guess he felt like a dumba--...
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Quoting TexasHurricane:


That is what I was thinking...they both (6 & 12) tend to play down storms..


Channel 6 definitely plays down storms. No over-hype there. I don't know anything about 12.

Thanks for the update, Homeless.

Just an off-the-wall question. Do any of you remember when Alison was just building up and Cary Cooper kept saying about it, "I'm not impressed." The newscaster kept asking, "Shouldn't we be worried?" "Could this be a problem?" and he just kept saying how unimpressed he was?
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1382. JRRP
Quoting mrnicktou:

Thanks so the new map is the updated one then?

no....
1:50 am
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Quoting StormW:
Ok folks, I'm out...back in the a.m.

Have a great evening.


Night Storm.
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Quoting iceman55:
Link


here new nam ooz


Wow. Lows galore! Lol.
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Quoting JLPR:
Freddy is not moving



almost appears to be moving SE....
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Quoting runnomore:


I see your point I was doing water rescues in the City of Friendswood with the fire department during Allison and a lot of the people were saying that Allison was worse but us old timers know better.


lol. i hear ya
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1372. Gumluvr
Quoting homelesswanderer:


Hi. yep I got the email you sent tonight. It's been raining real hard but off and on here. Hoping it's just rain. And like you say not too much of it. You may get some up there too. Greg said not everyone has gotten any yet. But 90% coverage for this weekend. Gonna be a wet one no matter what.


We have only had light showers today. Most of it has been to the south and over your way. I noticed Greg had up the chances of rain for this weekend.
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1371. JLPR
Freddy is not moving

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Whoa hey now they added a yellow blob at 10:45 of the Mid-Atlantic coast..!

Link
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Quoting iceman55:
11pm

Thanks so the new map is the updated one then?
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Quoting LPStormspotter:


i lived through both as well.. and it just depends on where you were at the time.. i live in Dickinson in 79 and Laporte in 01.. Didnt flood in 79 and did in 01.. ????


I see your point I was doing water rescues in the City of Friendswood with the fire department during Allison and a lot of the people were saying that Allison was worse but us old timers know better.
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Quoting TexasHurricane:


homeless - you have mail. :)


Thanks. And I agree. :)
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1365. hydrus
Quoting runnomore:


Yes it was and the rain gauge that recorded that was at FM 528 and the Clear Creek Bridge. Less than a mile from the house I lived in at the time. Clear Creek went out of its banks for over a mile. I remember walking thru 5’ of water in the street. Or in my case more like bobbing I was only 8 years old at the time.

It was far worse than Allison I don’t care what anybody says I lived thru both of them. Our house flooded in ’79 and did not even come close in Allison.
I remember both(even though I lived in Fl at the time) We had David later in 79. The flood damage in Houston was tremendous. That is probably why they say Allison was worse. I would bet Claudette had more rain.
Member Since: September 27, 2007 Posts: 1 Comments: 22683
Quoting runnomore:


Yes it was and the rain gauge that recorded that was at FM 528 and the Clear Creek Bridge. Less than a mile from the house I lived in at the time. Clear Creek went out of its banks for over a mile. I remember walking thru 5’ of water in the street. Or in my case more like bobbing I was only 8 years old at the time.

It was far worse than Allison I don’t care what anybody says I lived thru both of them. Our house flooded in ’79 and did not even come close in Allison.


i lived through both as well.. and it just depends on where you were at the time.. i live in Dickinson in 79 and Laporte in 01.. Didnt flood in 79 and did in 01.. ????
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Quoting runnomore:


Yes it was and the rain gauge that recorded that was at FM 528 and the Clear Creek Bridge. Less than a mile from the house I lived in at the time. Clear Creek went out of its banks for over a mile. I remember walking thru 5’ of water in the street. Or in my case more like bobbing I was only 8 years old at the time.

It was far worse than Allison I don’t care what anybody says I lived thru both of them. Our house flooded in ’79 and did not even come close in Allison.
Your last sentence nailed it. The only difference is Claudette's rain fell in the country, Allison in the city. If Houston had received Claudette's rain I hate to think how much worse things could have been.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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