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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1311. bappit
There were NNE winds at buoy 42020 (southeast of Corpus Christi) for several hours today but now they are ESE. Like something started to develop at the surface but like others point out it seems to be in the mid levels currently.
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Quoting btwntx08:

wow if that were to happen this blog would go crazy lol


What are you looking at?
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1309. hydrus
Quoting redwagon:


I know this sounds incomprehensible, but many areas in the drought zone NEED 35" of rain.

Just not in one day, of course. Which has been known to happen, almost, one place got 21" in one day.... in 1921, I believe?
I believe you, but believe me, if you get half that amount of rain in a short amount of time, there will be serious flash flooding. And it seems when ever they talk about rainfall over 10 inches, it is never the gradual or steady rain that occurs. It is still to early to determine how much rain Texas will get.
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I guess I meant non-cyclonic source of rain.

Four feet of rain in one day.... wow. Over what size area?
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Quoting winter123:
The northeast gale has now become non-frontal, with convection near the center. It is horribly sheared but it looks like a TD to me. Are the winds too low? what are they waiting for??




its too far N for it to me name a TD but how evere and un likey if they would and where too name it would have been a STD or STS
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Quoting geepy86:
Who set the GOM on fire?


Wasn't me.....
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Quoting geepy86:
Who set the GOM on fire?
Was only a matter of time...let's just pray it doesn't get too crazy
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Quoting Ameister12:
Good night, all!
Gonna leave you with the mm5fsu-gfs T=120 h.


ummmm.. what model is that
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1300. geepy86
Who set the GOM on fire?
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What does this mean?

http://manati.orbit.nesdis.noaa.gov/dataimages21/cur/zooms/WMBas13.png
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Quoting redwagon:


I know this sounds incomprehensible, but many areas in the drought zone NEED 35" of rain.

Just not in one day, of course. Which has been known to happen, almost, one place got 21" in one day.... in 1921, I believe?
Alvin, Texas. 42" in 24 hour period in 1979.
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btwntx can you please explain what you are seeing in that graphic/pic thxs
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This question is for Storm W. How far west do you think Fred will come. Is there a chance down the road for regeneration? The ridge looks like it will build pretty far west.
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Quoting hydrus:
Take it easy Superman, 35 Inches of rain is life threatening, and that area has been hit hard by drought. Why not try offering a little optimism.


I know this sounds incomprehensible, but many areas in the drought zone NEED 35" of rain.

Just not in one day, of course. Which has been known to happen, almost, one place got 21" in one day.... in 1921, I believe?
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The northeast gale has now become non-frontal, with convection near the center. It is horribly sheared but it looks like a TD to me. Are the winds too low? what are they waiting for??

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Quoting StormW:


Was the question for me?


who better to answer it?
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Quoting superweatherman:
I really smell other Tropical Storm Allison ...Yellow Circle!!!!!.... This not good for any town in the Texas Gulf Cost... what do you think 5, 10, ....35 in of rain?
Someone mentioned Claudette earlier. I was wondering if they were talking about Tropical Storm Claudette which hovered over southeast Texas in 1979. Produced 42" of rain in a 24 hour period for a record in the US.
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1286. hydrus
Quoting superweatherman:
I really smell other Tropical Storm Allison ...Yellow Circle!!!!!.... This not good for any town in the Texas Gulf Cost... what do you think 5, 10, ....35 in of rain?
Take it easy Superman, 35 Inches of rain is life threatening, and that area has been hit hard by drought. Why not try offering a little optimism.
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Good night, all!
Gonna leave you with the mm5fsu-gfs T=120 h.
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No name for the NE Coastal Storm?, huh! I've already coined it the "9/11/09 Storm". SO THERE!!!
lol!!!
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Thanks Storm! post #1247
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The Jersey Shore looks like its going to take it on the chin. Tropical Storm conditions already. I'm making a youtube.com video, and will let you know when it "drops", within the next few hours. BTW...TWC's Nicole Mitchell looks like she has had work done. Oh no, Seidel is in Avalon, not far from me!!!
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Nice Convention...(well apocalyse ain't here)
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Quoting KEEPEROFTHEGATE:


iam pegging it at mark 24.1n/95.4w
latest still ir image


latest anmin image


it's interesting to see how it begins at the coastline, then starts developing more over land. but maybe it has been doing that all along.
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I am so new at this. If you have the time, can you tell me how to read that? I get the basics but...
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Tomm morning/afternoon flare up will tell the tale whether or not it's gonna do anything
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Quoting pcolasky:


For us girls it = big hair


ha big hair is fun, in the 70's haha
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I really smell other Tropical Storm Allison ...Yellow Circle!!!!!.... This not good for any town in the Texas Gulf Cost... what do you think 5, 10, ....35 in of rain?
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Quoting StormW:


If a low develops, or let's say, if that yellow circle is centered wher they think a low may form, then it may have enough time over water to take advantage of, if the shear forecast is right, any favorable upper level winds.


That's what I was afraid you meant..okay..I'll tune in the morning. G'night all. Thanks Storm.
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Quoting Bordonaro:

No closed circulation yet folks!!


scratch that, thats this morning's pass
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1263. KEEPEROFTHEGATE (Mod)
Quoting hurricaneseason2006:
Some of you guys ar e wishcasting this GOM storm and it has nothing to do with rain since you getting it anyway. Some of you are wishcasting this to develop.
iam not wishcasting nothing but at the moment a good rain maker with poss tropical depression or storm status by sun 13 of sept if everything plays out right nothing wrong with making one aware of poss dev of a system hopefully nothing but its the tropics and it mid sept anything can happen and proably will this is a wait watch see run
Member Since: July 15, 2006 Posts: 171 Comments: 53809

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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.