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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The models were consistent this week about developing a "strong low" off southeast TX moving NE to Southern Louisiana. This was the forecast the whole wk. Track to TX within the last 24 hrs.
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BBL after the NFL game....
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Quoting Weather456:
Shear has decrease quite a bit from what it was early this week...I'm not sure if it will be reintroduced into the region.



456, do you think there is a chance for that blob to develop in the GOM?
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1108. amd
Quoting laflastormtracker:
Is anyone not convinced this system is going to TX? The whole week the CMC then NAM were indicating south of Lafayette, then last night and today, TXLA border then Houston, not convinced of the more western track...yet. Anyone has related thoughts? Reasons for a west shift?


My non-expert opinion is that the models expect a low to form very close to the Texas coast, if not that, over land.

However, the Brownsville NEXRAD radar may be telling a different story. A low pressure is trying to develop about 50 miles offshore, and it is drifting to the east. But, upper level winds are still unfavorable, at about 20 to 25 knots.

Link

Link
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Shear has decrease quite a bit from what it was early this week...I'm not sure if it will be reintroduced into the region.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting btwntx08:

lp thats what iceman is saying shear is decreasing in the western gom


lol. ok I thought he was saying still high there.
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1104. Dakster
Quoting iceman55:
The next Katrina in the making....?


I know it has little chance of doing that, my point was that no one knows yet what is going to happen to the yellow area in the GOM. Kind of like the next Atlantic Hurricane to hit CONUS will hit somewhere between Brownsville, TX and Maine.
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Is anyone not convinced this system is going to TX? The whole week the CMC then NAM were indicating south of Lafayette, then last night and today, TXLA border then Houston, not convinced of the more western track...yet. Anyone has related thoughts? Reasons for a west shift?
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And I appoligize for the mispelled words. ;)
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1099. Dakster
Quoting btwntx08:

huh????


The yellow GOM Circle. Could be nothing, could be something...
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Quoting iceman55:
btwntx08 .20k sheer and go down


Im sorry what do you mean? Our local said shear has moved from that area in the GOM. said high shear is now over FL
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I would love to view shear charts for the gulf...unfortunately I have lost my contacts and quiet honestly cant see anything. So can someone tell me what the chances are the AOI develops?
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1095. Dakster
Iceman???
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1094. Dakster
And no storm prior to Fred was ever a Cat 3 as South and East as he was... Hmmmm... Never say never.

When was the first time in snowed in Miami? (I know the last time it snowed, which was in 1975.)
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Quoting btwntx08:
if this going to develop i would look east to ese of brownsville cause it look suspcious there


That's where my local said to look too.
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Quoting StSimonsIslandGAGuy:
Number of storms north of 20N and east of 40W that have later made landfall in the USA or the Caribbean?

Zero.


Ike was close. But they said no storm ever where he was (at one point) had ever made it into the gulf. So theres always a first I guess.
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1090. Dakster
The next Katrina in the making....?

OR the next thunderstorm we track?
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Post 1078.
Good Post, and my thoughts exactly. Yes, science has improved immensly, but there is no way to be "sure" of the findings.
As a person who is familiar with the growth of trees in the wet season/dry season environment, and the signature left by tree rings that represent growth, I am dubious of this, too.
Some years, the tree, in certain environments (along watercourses, near ponds etc) shows next to no growth signature, due to dry spells, changes in waterflow direction etc.
Very interesting stuff.
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So, I leave for a few hours, and pop back in, and now we have a yellow circle?? Whats up with that??
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1085. Brillig
Quoting zoomiami:
Is the rain in Texas in an area that will help with the drought?


Definitely!
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Very strong Shear is about to wack Fred beside the head from the SW..

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1079. Brillig
Quoting K8eCane:
i dont understand why we get tropical storms? no place in the US is considered tropical except maybe extreme south fla


And if you look at a map of tropical storms and hurricanes, they mostly miss the tropics.
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Holy crap, yellow and stationary for a few days?? GOM***
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1076. Patrap
Quoting indianrivguy:
Pat.. do you save any of those? A couple years back I started trying to capture landfall loops, not only radar but velocity too. It may even have been you that got me looking at the doppler because you post them time to time. I found them interesting and syatyed including them. Anyway.. things seem to happen quick on the Texas coast, and I've learned to start saving early. And on this one, like you, I've been watching for rotation all day.


Some Loops I save to photobucket,but the wu radar are archived now and that makes it a lot easier to refer back to a specific event.
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Quoting laflastormtracker:
Yep. And we get them night crawlers too. Spooky. ;)

Night is alright as long as i am not home alone...lol


Lol. I just aint home. :) Well, if we get warning. Lol.
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Yep. And we get them night crawlers too. Spooky. ;)

Night is alright as long as i am not home alone...lol
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Pat.. do you save any of those? A couple years back I started trying to capture landfall loops, not only radar but velocity too. It may even have been you that got me looking at the doppler because you post them time to time. I found them interesting and syatyed including them. Anyway.. things seem to happen quick on the Texas coast, and I've learned to start saving early. And on this one, like you, I've been watching for rotation all day.
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no apparent LLC yet
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Quoting laflastormtracker:
You know homeless to that same extent when i was growing up i thought the NW Gulf was a quite place tropically...now pssssh i realize geez was i ever wrong! what i learned- almost anything has potential to spin up and move very slowly as this system is forecast to, ie. Rita took 48 hours to move thru- 2 days of humid cloudiness and rain :P


Yep. And we get them night crawlers too. Spooky. ;)
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1. WIDESPREAD SHOWERS AND THUNDERSTORMS OVER THE NORTHWESTERN GULF OF
MEXICO ARE ASSOCIATED WITH A SURFACE TROUGH INTERACTING WITH A MID-
TO UPPER-LEVEL LOW. UPPER-LEVEL WINDS ARE EXPECTED TO REMAIN
UNFAVORABLE FOR DEVELOPMENT OF THIS SYSTEM AS IT REMAINS NEARLY
STATIONARY NEAR THE TEXAS COAST DURING THE NEXT COUPLE OF DAYS.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. REGARDLESS
OF DEVELOPMENT...LOCALLY HEAVY RAINFALL IS POSSIBLE ALONG THE GULF
COAST FROM NORTHEASTERN MEXICO TO LOUISIANA OVER THE NEXT DAY OR
TWO.
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1045. Zoomiami - I noticed the same thing out in western Broward. Yesterday driving back from lunch, I went in and out of rain storms four times in about 2 miles. It came down hard and fast...on and off..all day. Very strange. It was almost squally weather.
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Areas of Interest (AOI)
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Thank you 456. So anything can happen!!!
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You know homeless to that same extent when i was growing up i thought the NW Gulf was a quite place tropically...now pssssh i realize geez was i ever wrong! what i learned- almost anything has potential to spin up and move very slowly as this system is forecast to, ie. Rita took 48 hours to move thru- 2 days of humid cloudiness and rain :P
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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.