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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Quoting StormW:
Anyone know the significance of this?



It shows a extreme drop in Surface Pressure in a short period of time and looking over a 4 day span as an average. End result! We have a Surface Low!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
1860. ackee
Quoting stormpetrol:
I think an area in the SW Caribbean might bear watching.
agree THINK THAT THE ONLY PLACE LOOKING 4 development now
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1859. IKE
Quoting StormW:


We have a winner!

Thanks IKE!


If it wasn't tropical you wouldn't see the winds drop off to near zero as the "center" went over this buoy.

Should have been designated.
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850mb vorticity-- I don't see any where the disturbance is supposed to be
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"Anyone know the significance of this?"

Looks like a surface center has formed. Drop in pressure, change in wind direction...

If true, then the COC is over water which is not good...
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Thanks Storm! I am going check that out! Was hoping that didn't come from a buoy in the GOMEX
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1854. ackee
the 2009 seasons comeing to end my thinking we see two more name system my view
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increased surface low prob? (guessing)
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I hate to ask, but is that in the GOM?
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Quoting TheCaneWhisperer:


I am confused


the females dont look like recurves to me, not at all. personally I am not gonna count storm "one" as it doesnt have actual name.

and the models had fred doing backflips two days ago we believed them then. why is it now out of the question that it would trend west over north or northeast?
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1849. IKE
Quoting StormW:
Anyone know the significance of this?



Looks tropical to me.
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Quoting StormW:
Anyone know the significance of this?



Where is that bouy?
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The only reason the others didn't re-curve is because they we're weak storms. Claudette is the only one that didn't have a chance.
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I think an area in the SW Caribbean might bear watching.
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Quoting CandiBarr:


well yeah, look at the map. what about the ones that didnt recurve. there are just as many that didnt as did.


I am confused?

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And I agree with the past doesn't determine the future statement but, one can be skeptical of a persistent weather pattern.
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I'm out. Gotta date with a fishing pole.

"Women love me. Fish fear me."
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Quoting P451:
Northern reach of the arc of precip has begun to reach me. Wind definitely picked up now. Consistently gusting 35-40. Had one that had to be pushing 50 again as several live 1/8th inch twigs got ripped off every tree within sight. Numerous leaves of course got ripped down with that one. A few dead 1/4 inch thick limbs came down as well. So I'd say about 50mph.

We don't yet have a sustained wind per say as we get lulls that are down to 10mph or less - again - not very tropical like - more winter gale like.

Still cold and wet - not warm and sticky as it is when TS's get up here. Again, waiting to see what happens after this arc of precip.

I'm sure this storm has hybrid characteristics but there is something to be said for ground observations by those going through it. Right now? It's just a gale to me. We'll see as we get under the influence of the core if the weather changes to a more tropical nature or not.


Are you in Delaware area??? Is there going to be bad weather all weekend? I am heading up that way today.
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Quoting TheCaneWhisperer:


I wasn't referring to conditions inhibiting cyclones. I was referring to the persistent troughing pattern that has been in place on the east coast this summer and re-curving any cyclone that tries to make it too the US Coast. You dis-agree with that??????


well yeah, look at the map. what about the ones that didnt recurve. there are just as many that didnt as did.
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Quoting CandiBarr:


i have to respectfully disagree. Id say that its currently 50% trough 50% shear. either way, the past doesnt determine the future.



I wasn't referring to conditions inhibiting cyclones. I was referring to the persistent troughing pattern that has been in place on the east coast this summer and re-curving any cyclone that tries to make it to the US Coast. You dis-agree with that??????
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1838. Dakster
Quoting BobinTampa:
Good morning everyone. Always sad thinking back to 8 years ago and what took place. Never forget that day.



Yep. I will never forget what I was doing or where I was at...
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Quoting yonzabam:


The troughs have ruled because of the unusually southerly position of the jet stream. It was over Scotland during July/August, bringing us a very wet summer, with the remnants of Bill and Danny thrown in for good measure.

It's now moved north to Iceland and we have some sun here, for a change. I'd expect some northward movement from the westward region of the jet stream, too. So, the prediction that there will be ridging instead of a trough looks like a pretty solid bet to me.


That could make for an interesting end of the season.
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Quoting TheCaneWhisperer:


While I agree with that scenario IF ridging were to take over, ridging has been forecast to take over for some time now and, as we have witnessed time and time again, trough's rule the stage.


i have to respectfully disagree. Id say that its currently 50% trough 50% shear. either way, the past doesnt determine the future.

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Good morning everyone. Always sad thinking back to 8 years ago and what took place. Never forget that day.

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Quoting caneluver:


And why do you have to be a smart a@# this morning?


this morning alone? i was born that way :)
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P451, Fair enough brother, I did not suffer any personal losses, my condolences to you, and those that did. I hold in my heart the greatest of sorrow for the innocents we lost, and the highest of regards and honor for those going up when things came down. No harm meant.
Member Since: September 23, 2006 Posts: 1 Comments: 2587
Quoting P451:
Yeah, now we're getting into it. One good blast of thunder and the lights are now dimming on and off. Another wind gust pushing 50 for certain just ripped down more stuff from the trees and I hear someone's roof flashing clanking in the wind now.


hey P where you at, the disturbance on the northeast US coast?
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Heres the latest JB thoughts.


FRIDAY 7 AM
NOAA WEATHER RADIO KNOCKED OFF THE AIR... BUT WE HAVE HAVE KYW AND ELLIOT IN THE FIRST PLACE!

At the height of the storm... the flame throwing newstalk powerhouse of the Delaware valley is blasting the accuweather message into the storm area, so fear not huddled masses. we are with you!

I wonder why it got knocked off the air

The severe thunderstorm warnings are not because these are severe in the classic sense, but that the turbulent mixing in the banding allows the wind ( the vada has 65kts over south Jersey at 3k) to come down to the surface. SO this is tropical cyclone, banding created wind with thunderstorms going off because of the intense upward motion in the bands, caused by NON BAROCLINIC PROCESSES, but instead low level forcing which reaches its peak around the center. One can not help but notice there are strong winds near the center that steadily increase until the center comes over you.. as in a warm core cyclone.. which this is.

I have seen no storm reports out of Mt. Holly. Cmon guys, Taunton would have been had one out every three hours.. We may not be able to hear you, but we still love you.

Its just that we love Elliot more.

K-Y-W..News Radio.. 10-60

You can tell I am punch drunk from being up.. I am singing the KYW jingle to myself

ciao for now *****
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Local Update:

Heavy Rainfall Possible Through Sunday

New model data this morning continues to point towards a tropical low (depression) or hybrid low developing near Brownsville and moving northeast through the weekend bringing torrential rainfall.

Deep atmospheric moisture remains entrenched across the area and and upper-level low over Central Texas will keep the chance for heavy rainfall in the forecast. Two inche per hour rainfall rates could easily produce street flooding. Remember, to turn around and not drown or risk costly damage to your vehicle - is it worth it? Highs today will climb to the lower-eighties.

Tonight, heavy rainfall will continue in the forecast with patchy fog and lows in the middle-seventies.

Saturday and Sunday will be wet as low pressure moves toward our area bringing torrential rainfall and breezy weather conditions. Highs may not get out of the seventies with nearly a one-hundred percent chance of heavy rainfall.
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1825. Dakster
Quoting IKE:


Rain over the SE USA isn't going away anytime soon. The GOM is loaded with convection.

I thought it was a downward MJO?


The rain is coming DOWN...
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Quoting TheCaneWhisperer:


I am curious to see what the steering will be down the line if it were to maintain TS storm status and not degenerate into a remnant low. Fred's already a record breaker and I tend to pay a little more attention to those types.


probly would not go as west as it is forecasted to
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Quoting reedzone:
Honestly, the GFS may not be too far off with bringing the remnants of Fred to the USA. If the models are right, the "monster troughs" will come to a halt for a while and building ridges may take place next week, which steers storms west. So the area that just came off Africa, that one has a chance to be affected more by a ridge then a trough.


isnt the nao or mjo - one of those special things i dont get - going to shift right about mid-late september?
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1819. JRRP
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Quoting caneluver:
Most models are looking scary for the CONUS


yeah... 20knot remnant low heading towards the US has the coast heading to their evacuation shelters
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Quoting TheCaneWhisperer:


While I agree with that scenario IF ridging were to take over, ridging has been forecast to take over for some time now and, as we have witnessed time and time again, trough's rule the stage.


The troughs have ruled because of the unusually southerly position of the jet stream. It was over Scotland during July/August, bringing us a very wet summer, with the remnants of Bill and Danny thrown in for good measure.

It's now moved north to Iceland and we have some sun here, for a change. I'd expect some northward movement from the westward region of the jet stream, too. So, the prediction that there will be ridging instead of a trough looks like a pretty solid bet to me.
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Quoting IKE:


Rain over the SE USA isn't going away anytime soon. The GOM is loaded with convection.

I thought it was a downward MJO?


Then we better all buy boats, JFV included when upward pulse comes.
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Morning everyone.

Yea Tim, it is, and it all began to go down about this time of the morning.
Member Since: September 23, 2006 Posts: 1 Comments: 2587

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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.