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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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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I smell other Allison but in south Texas
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Quoting zoomiami:
Orca - there you are with the green blobs again!

Thought of you the other day - there was a pic of a BIG mean orca eating the penguins....


Penguins are good, especially BBQ :)
God knows they can't play Hockey
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting laflastormtracker:
homeless, so you think this thing whatever it is will landfall Sunday the 13th? LOL


:P
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Quoting hailcatcher:
Hello long time jer..,uh, oops...lurker and obviously new poster/...troll? Has a tropical cyclone ever formed from an outer band of another tropical cyclone - a seperate wave from a hurricane or TS?


remnant tails of hurricanes can create cyclogenesis of the tropical nature.
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Based on IKE's post #1030, I'm going to say the weather moving in on the weekend is due to the blob off of the Texas coast.
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homeless, so you think this thing whatever it is will landfall Sunday the 13th? LOL
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I'm in Cedar Park, TX (south central draught-stricken, water restricted texas) and it's RAINING!!!!!! Thank you tropics gods!
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Quoting Weather456:


sure it was expected to happen, normally thats how develop occurs in these situations, you have a surface trough or low of some sort, interacting with a nearby upper trough or low to produce scattered showers. Then as these showers develop you get a positive feedback loop that leads to development if conditions allow for it. Here, proximity to land and upper winds may be contenders. so we'll see how that goes.

Yesterday

I have analysed some model data and seems reasonable that a disturbance may form across the Gulf of Mexico later this weekend. Genesis originates from a short-wave that digs across the South-Central United States


Thanks...Right Now conditions are not all that favorable for development...So I agree with the NHC that any development would be slow...:D
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Quoting hailcatcher:
Hello long time jer..,uh, oops...lurker and obviously new poster/...troll? Has a tropical cyclone ever formed from an outer band of another tropical cyclone - a seperate wave from a hurricane or TS?


Hurricane Gordon 2006

The initial development of this system can be linked to Hurricane Florence. It began as a tropical wave immediately behind Florence in the first week of September, which initially was absorbed into the enormous circulation of then-Tropical Storm Florence. As Florence began to organize and move northwest, the wave managed to break from the circulation again and gradually organize despite initially hostile conditions. On September 10, it had organized enough to be declared Tropical Depression Seven northeast of the Lesser Antilles.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Orca - there you are with the green blobs again!

Thought of you the other day - there was a pic of a BIG mean orca eating the penguins....
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Is the rain in Texas in an area that will help with the drought?
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AOI

AOI

AOI

AOI

Member Since: October 1, 2007 Posts: 81 Comments: 26511
Hello long time jer..,uh, oops...lurker and obviously new poster/...troll? Has a tropical cyclone ever formed from an outer band of another tropical cyclone - a seperate wave from a hurricane or TS?
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Quoting cyclonekid:


So u r saying that that is what it is expected to do....just asking??? Trying to learn...:-)


sure it was expected to happen, normally thats how develop occurs in these situations, you have a surface trough or low of some sort, interacting with a nearby upper trough or low to produce scattered showers. Then as these showers develop you get a positive feedback loop that leads to development if conditions allow for it. Here, proximity to land and upper winds may be contenders. so we'll see how that goes.

Yesterday

I have analysed some model data and seems reasonable that a disturbance may form across the Gulf of Mexico later this weekend. Genesis originates from a short-wave that digs across the South-Central United States
Member Since: July 24, 2005 Posts: 407 Comments: 19076
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Yesterday at 11:40PM the National Weather Service radar was struck by lightning, it is currently down, for those of you wondering. Fred continues to weaken, and should not affect any land, Fred should be dissipated in about 72 hours. I am watching an area of low pressure in the Golf of Mexico, I think this could become our next TD, other than that there are some vigorous waves emerging and over Africa. Right now the Atlantic is very quiet for being in the exact peak of Hurricane season.
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1046. Patrap
Member Since: July 3, 2005 Posts: 424 Comments: 128344
Surface observations: we have had some of the strangest weather here - storms are not at 3:00 pm - lots in the evening. A lot of rain, and high chance of pop for a series of days, again unusual.

Lake Okeechobee is at 14.34 ft - without a tropical system. They would have to let water out if we did get one.

The atmosphere is not at all in the normal pattern for south florida.
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Quoting Samantha550:


Been working all day, hopefully we will not have a Humberto type situation. I think I will go with Greg since 12 had there precip levels at 40% last night and Greg has been calling it all along.


Yeah, I know what you mean. Channel 12 upped it to 60-70%. Greg upped it to 90% both days. Its pouring here already. They said on the news streets and homes were already flooded but didn't say where.
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Quoting Hurricane009:
I am not forcing anybody to go to tropics chat. I was merely asking!! geesh


lol
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Quoting Weather456:


the surface trough over the GOM is interacting with the shortwave over Texas.


So u r saying that that is what it is expected to do....just asking??? Trying to learn...:-)
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Quoting StormW:


And actually, though NAM may not be the best for cyclogenesis, I've noticed the past 3 seasons, believe it or not, it can be fairly accurate with track or showing where moisture/precip is going to be.


StormW as i have said when i use the NAM its only good out to 48hrs IMO to do exactly as you very well stated.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting cyclonekid:
Is that what it is doing now??


the surface trough over the GOM is interacting with the shortwave over Texas.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting watcher123:
No clue on that one.

It baffles me how people claim to know what an ice pack looked like 2000 years ago, but they can't even predict this hurricane 1/100th as accurately as they claim to date a layer of ice or dirt.

No offense, but nobody here is 2000 years old, so how can anyone claim to know what the ice looked like?

They drill core tubes and bring them up and analyze the old ice to determine all sorts of cool things (pun intended).
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Quoting homelesswanderer:


Hi. Ok just watched the locals better post before I forget. :)

Ch 12 said that right now it is just a rainmaker. And if there is development they will let us know because they won awards last year for their Ike coverage. Lol. Tooting his own horn. He said 15 mph winds.

Greg said its still on land. Looks to move east into the gulf. Any development would be slow. Should slowly move up this way. And its going to be a frog strangler. Heck, it just started pouring here again! Anyway he said he'd be very surprised if it got more than 40-45 mph tropical storm.

Lol. I guess take your pick. I'll wumail you Tex if you're not still on. :)


Been working all day, hopefully we will not have a Humberto type situation. I think I will go with Greg since 12 had there precip levels at 40% last night and Greg has been calling it all along.
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1036. Patrap
Its amazing what we can google and Learn in 30 secs,..LOL


Ice Core and Air-Snow Exchange Research and Coordination


The recovery and analysis of ice cores from glaciers around the globe and related studies of air/snow exchange have been a research foci for the Climate Change Research Center for the past two decades.

More here..
Member Since: July 3, 2005 Posts: 424 Comments: 128344
1034. IKE
SYNOPSIS FOR THE GULF OF MEXICO
430 PM CDT THU SEP 10 2009

.SYNOPSIS...A WEAK TROUGH OVER THE SE GULF WILL DRIFT NW TONIGHT
AND LOSE IDENTITY OVER N CENTRAL GULF LATE FRI NIGHT. LOW PRES
WILL DEVELOP NEAR 28N97W ALONG A COASTAL TROUGH FRI. THE LOW
WILL MOVE N ON SAT AND SUN TRAILING A WEAK COLD FRONT OFFSHORE
TEXAS COAST SUNRISE MON. THE FRONT WILL STALL FROM THE
MISSISSIPPI DELTA TO SE TEXAS TUE NIGHT.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Thanks Ike. :)

Well its official...We are going to get wet. :)
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Quoting Hurricane009:
Tropics Chat... Anyone... Please??



Please dont fores bloger too go too Tropics Chat!
Member Since: May 21, 2006 Posts: 5091 Comments: 115131
In Pensacola here. We have an 80% chance for rain on Saturday. Is this going to come in from the West or the South?
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1030. IKE
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting Weather456:
Genesis starts with a negatively tilt shortwave

Is that what it is doing now??
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Quoting IKE:
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT THU SEP 10 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON HURRICANE
FRED...LOCATED ABOUT 740 MILES WEST OF THE CAPE VERDE ISLANDS.

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.


ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.



Yet the models are developing it, interesting. NHC doesn't think much of it obviously.
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1024. JLPR


Weak low continues to quietly exit Africa xD

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Quoting StormW:


:)

Evening 456.

Correct. Hence North AmericanMesoscale model


Evening Chief
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1022. IKE
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT THU SEP 10 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON HURRICANE
FRED...LOCATED ABOUT 740 MILES WEST OF THE CAPE VERDE ISLANDS.

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.


ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting TampaSpin:


I fully agree and understand what you are saying. The AOI that i pointed out is what it is especially around the GOM. ONe and only one would become the dominate feature there. The AOI in the South Caribbean i showed will travel across the Yucatan and could have a chance of developing in the GOM near the BOC. Sorry if i didn't make bullets as to why i showed each AOI. Oh well, Its just my Opinion any how. What the heck do i know.


Well said. And I agree.
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Quoting StormW:


And actually, though NAM may not be the best for cyclogenesis, I've noticed the past 3 seasons, believe it or not, it can be fairly accurate with track or showing where moisture/precip is going to be.


Hi Storm. And I hope the Nam is wrong this time. Lol. :)
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Quoting StormW:


I don't have one.

I know and you've proven yourself time and again regardless =] I like the fact you don't to be honest. You keep it in terms most can understand, simple physics alot of times. While the specifics lie in the math ( as with any science ) the overall view is still quite accurate and I like to see what you say pattern wise as well as put my own maths into it. So that the next time i see a pattern I don't have to work the math again =] You've earned your spot in the meteorological community more than many of us combined ( degreed or not)
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Quoting StormW:


And actually, though NAM may not be the best for cyclogenesis, I've noticed the past 3 seasons, believe it or not, it can be fairly accurate with track or showing where moisture/precip is going to be.


In addition, its a regional or sub-synoptic scale model trying to resolve synoptic scale disturbances, ie, tropical systems.
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1015. Patrap
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Quoting SouthALWX:
lets not get into the my degree is better game please. PSU is a reputable university though it's course of study is geared for uppergrad stuff ( I plan to go there upon completing my own undergrad) I understand both points and the fact is that the models are an either or not both scenario. If one or two areas form it drastically limits the opportunity for the others to form. That being said I think its fine to label them AOI but at the same time it's all but impossible they all develop and I can definitely see 456's point. Rather than just AIO it would be far more useful if you provided a probability on them. If you are using strictyl model guidance use an x/y format where x is the number of models developing the aoi and y is the number of models under your consideration.


I fully agree and understand what you are saying. The AOI that i pointed out is what it is especially around the GOM. ONe and only one would become the dominate feature there. The AOI in the South Caribbean i showed will travel across the Yucatan and could have a chance of developing in the GOM near the BOC. Sorry if i didn't make bullets as to why i showed each AOI. Oh well, Its just my Opinion any how. What the heck do i know.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting mrnicktou:

he was quoting somebody talking about extra-tropical storms and were trying to get a grasp on the storms in the gulf so keep yourself from going off topic because some of us live in SE texas


And some of us live in Nova Scotia...
... Cheers!
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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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