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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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: 174 Comments: 54450
East Conus NH IR Loop:

Link

I dont know how to post a loop. I think this is one i saved from pat, thx pat :)
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1260. surfmom
Quoting Patrap:
Best to keep a wary eye on this one.. Its in a Good Spot and has some real Flavor seems.



I hear you Patrap...
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.
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Quoting StormW:


No development overnight..nope.

:) Thanks. I need sleep.
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Quoting tornadodude:
here ya go


For us girls it = big hair
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Quoting btwntx08:

oh yea on the winds in brownsville if it were at the surface then the wind should be ne but its only mid level right now


I'm happy you understand now :P
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Quoting Bordonaro:


NVRM
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Quoting StormW:


That's centered where we don't want it centered.

um, splain please Chief :)
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Quoting RitaEvac:
Weather456 if for some reason that turned out to be the primary low (hope not) then TX is gonna miss out on a lot of the rain, because it's already too far offshore and the rain/convection will tend to focus closer near the circulation. If TX wants a lot of rain then it needs to stay as is so the rain is widespread and unorganized over large real estate. Now if one forms much closer to the coast then still would get plenty of rain...




therefore the importance lies where the low track and not tropical storm development. Choose 1, development or rain, remaining undeveloped along the coast is more ideal for Texas.
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here ya go
Member Since: June 28, 2006 Posts: 25 Comments: 8360

No closed circulation yet folks!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Thanks IKE!
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Quoting StormW:


If a low forms closer to the coast or just inland...shouldn't be too much.

IF we get a low farther south and a center gets over the water and stays for about 24 hours or so, then something could spin up. Maybe not quickly, but the upper level winds are supposed to become more conducive in about 48-72 hours. Although not optimal as far as outflow, though there will be some slight ridging north of the area, the winds are forecast to relax to favorable, and with the water as warm as it is, something could spin up. May still not be too much as the area (GOMEX) is under strong downward motion of the MJO, but good to watch it.

Heya Storm - so I can go to sleep tonight and nothing will "develop", right?
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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.


Not at all models support a weak tropical or extratropical development over the next few days, and one thing is sure SST are the warmest in the atlantic basin in that area (GOM). just need a sfc Low and there is one appears to be forming as we type.

As of to Fred he is becaming strationary. A turn to the WNW or even W is more reliable forrescast as pointed out a week ago by Weather 456 and Storm W, over time the key will how much time he stay stationary before start to move.
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1242. Gumluvr
Thanks for the update Storm. Homeless you have mail.
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1241. Dakster
Thanks Stormw.
Member Since: March 10, 2006 Posts: 0 Comments: 10476
1240. Patrap
GOM 60 Hour Water Surface Temperature Forecast Model
Member Since: July 3, 2005 Posts: 426 Comments: 128710
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I see we now have the yellow circle......

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1236. Patrap
ESL site is Back Up after a T-storm outage to the server.

Member Since: July 3, 2005 Posts: 426 Comments: 128710
I know my friends in Houston could use some rain!
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1234. KEEPEROFTHEGATE (Mod)
Quoting StormW:


If a low forms closer to the coast or just inland...shouldn't be too much.

IF we get a low farther south and a center gets over the water and stays for about 24 hours or so, then something could spin up. Maybe not quickly, but the upper level winds are supposed to become more conducive in about 48-72 hours. Although not optimal as far as outflow, though there will be some slight ridging north of the area, the winds are forecast to relax to favorable, and with the water as warm as it is, something could spin up. May still not be too much as the area (GOMEX) is under strong downward motion of the MJO, but good to watch it.


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


latest anmin image
Member Since: July 15, 2006 Posts: 174 Comments: 54450
1233. IKE
Quoting pcolasky:


I was curious as to where are rain would be coming from this weekend; from the trough over Tx or the weather coming off of the West coast of Fl.


AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
236 PM EDT THU SEP 10 2009

.SHORT TERM (TONIGHT-SATURDAY NIGHT)...
THE MODELS ARE IN DECENT AGREEMENT OVER THE NEXT COUPLE OF DAYS AND
INDICATE THE UPPER LOW THAT IS CURRENTLY CENTERED OVER THE
MID-ATLANTIC STATES GRADUALLY LIFTING NORTHEAST THROUGH FRIDAY NIGHT
AS A ANOTHER UPPER LOW AND STRONG SHORTWAVE TROUGH DIGS SOUTHEAST
OVER THE NORTHERN PLAINS. MEANWHILE...ANOTHER UPPER LOW IS PROGGED
TO DEVELOP OVER EASTERN TEXAS FRIDAY NIGHT INTO SATURDAY...THEN LIFT
NNE...WHICH WILL ALLOW THE UPPER LEVEL WINDS TO BACK FROM NW TO SW
THROUGH THE DAY SATURDAY OVER OUR LOCAL AREA. THIS FEATURE WILL
RESULT IN CYCLOGENESIS SOMEWHERE NEAR THE TX COAST THROUGH THE DAY
FRIDAY WITH A WARM FRONT EXTENDING EAST ACROSS THE NORTHERN GULF.
FRIDAY NIGHT INTO SATURDAY...THE MODELS CONTINUE TO DEVELOP THIS
SURFACE LOW AND INDICATE A NNE TRACK INTO THE LOWER MS VALLEY COME
SATURDAY. THIS PATTERN WILL RESULT IN AN OVERRUNNING EVENT WITH THE
SOUTHWEST FLOW ALOFT AND THE WARM FRONT LIFTING NORTH TOWARD AND
OVER THE AREA. INCREASING RAIN CHANCES FRIDAY NIGHT THROUGH SATURDAY
NIGHT OVER THE LOCAL AREA WILL BE EXPECTED. PWAT VALUES WILL
INCREASE TO ABOVE THE TWO INCH MARK THROUGH THE DAY SATURDAY. THE
AVERAGE MODEL RAINFALL ACCUMULATION TOTALS THROUGH THE WEEKEND RANGE
FROM AROUND 1-3 INCHES OVER THE FORECAST AREA. LOCALLY HIGHER
AMOUNTS OF 2-4 INCHES WILL NOT BE OUT OF QUESTION DURING THIS
PERIOD.
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Quoting Patrap:
Best to keep a wary eye on this one.. Its in a Good Spot and has some real Flavor seems.


Nice circulation.
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I gotta go get my minni me in bed. Will check on things in the morning. Hope everyone has a great night!!
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Quoting btwntx08:
ok if that were to be the low then brownsville should of recieved ne/ene winds but its not the wind is coming from the ese


The general mid-upper flow east of Brownsville, TX is easterly - maybe slightly north or south thereof but the flow is easterly. Rita was saying that the low seen on water vapor imagery is mid-level and it seems reasonable since there is no surface low yet or any 850 vort.
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1229. Patrap
Best to keep a wary eye on this one.. Its in a Good Spot and has some real Flavor seems.

Member Since: July 3, 2005 Posts: 426 Comments: 128710
Quoting tropics21:
any storm can a rotation on Radar the question is is the spin on Sattelite? so far no

Example:
Not spinning. Or, is it?
Key West Radar Loop
Radar AMX still down.
HPC "Loop of sea-level pressures and fronts through day 7"
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Quoting IKE:
Vorticity...SE GOM....



I was curious as to where are rain would be coming from this weekend; from the trough over Tx or the weather coming off of the West coast of Fl.
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Weather456 if for some reason that turned out to be the primary low (hope not) then TX is gonna miss out on a lot of the rain, because it's already too far offshore and the rain/convection will tend to focus closer near the circulation. If TX wants a lot of rain then it needs to stay as is so the rain is widespread and unorganized over large real estate. Now if one forms much closer to the coast then still would get plenty of rain...

Member Since: July 14, 2008 Posts: 1 Comments: 9630
10 5:30 pm ESE 19.4 21.4 - - - - 29.91 - 74.8 85.1 70.3 - - -
09 10 5:00 pm E 15.5 19.4 - - - - 29.92 -0.03 74.8 85.1 69.8 - - -
09 10 4:30 pm E 7.8 11.7 - - - - 29.93 - 74.8 85.1 70.3 - - -
09 10 4:00 pm ESE 13.6 15.5 - - - - 29.92 +0.00 74.8 85.1 70.7 - - -
09 10 3:30 pm E 13.6 15.5 - - - - 29.92 - 72.7 84.9 70.0 - - -
09 10 3:00 pm SE 9.7 15.5 - - - - 29.95 - 73.0 85.1 70.0 - - -
09 10 2:30 pm E 9.7 13.6 - - - - 29.95 - 73.0 85.3 70.2 - - -
09 10 2:00 pm S 21.4 25.3 - - - - 29.95 +0.01 74.8 85.5 70.9 - - -
09 10 1:30 pm NNE 9.7 13.6 - - - - 29.92 - 80.2 85.5 69.8 - - -
09 10 1:00 pm NE 9.7 13.6 - - - - 29.92 -0.02 80.6 85.5 71.6 - - -
09 10 12:30 pm NE 9.7 11.7 - - - - 29.92 - 80.1 85.5 70.0 - - -
09 10 12:00 pm NNE 7.8 11.7 - - - - 29.92 +0.00 80.2 85.5 70.2 - - -
09 10 11:30 am NNE 5.8 7.8 - - - - 29.94 - 79.5 85.5 69.1 - - -
09 10 11:00 am N 5.8 9.7 - - - - 29.94 - 79.7 85.3 70.2 - - -
09 10 10:30 am NNW 5.8 7.8 - - - - 29.93 - 78.8 85.3 69.8 - - -
09 10 10:00 am - 0.0 1.9 - - - - 29.94 - 79.5 85.3 66.6 - - -
09 10 9:30 am ENE 3.9 5.8 - - - - 29.93 - 79.2 85.1 70.0 - - -
09 10 9:00 am ENE 5.8 7.8 - - - - 29.93 +0.05 78.1 85.1 71.1 - - -
09 10 8:30 am SSE 3.9 5.8 - - - - 29.91 - 77.4 85.3 70.9 - - -
09 10 8:00 am SSE 7.8 7.8 - - - - 29.91 +0.03 76.5 85.3 69.1 - - -
09 10 7:30 am S 5.8 7.8 - - - - 29.91 - 74.7 85.3 68.2 - - -
09 10 7:00 am SSW 21.4 29.1 - - - - 29.91 +0.03 77.5 85.3
Data from nearest buoy to convection rotation off Brownsville coast
Member Since: September 8, 2008 Posts: 1 Comments: 1078
mm5fsu-gfs are picking up on a monster GOM storm and another Cape Verde hurricane/tropical storm.

mm5fsu-gfs
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1219. WxLogic
Quoting StormW:
Evening!


Hi...
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1218. Patrap

NEXRAD Radar
Brownsville, Storm Relative Mean Radial Velocity 0.50 Degree Elevation Range 124 NMI


Member Since: July 3, 2005 Posts: 426 Comments: 128710
Good evening, everyone!
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1215. Dakster
STORMW! Sorry I missed you on BOB tonight. What's your take on the GOM?
Member Since: March 10, 2006 Posts: 0 Comments: 10476
Quoting StormW:
Evening!


'Evening chief!
Member Since: June 28, 2006 Posts: 25 Comments: 8360
Quoting btwntx08:

shear is decreasing


he's taking about about the mid-upper winds blowing the mid-level vort east which is evident through vapor winds



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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.