CSU and TSR continue to predict a near-average hurricane season

By: Dr. Jeff Masters , 3:18 PM GMT on August 04, 2009

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A tropical disturbance embedded in the Intertropical Convergence Zone (ITCZ), near 9N 35W, is moving west at about 15 mph. The heavy thunderstorm activity associated with this tropical wave has changed little over the past 24 hours, and remains disorganized. This morning's QuikSCAT pass showed a moderate wind shift, but nothing resembling an organized surface circulation. Top winds were in the 20 - 30 mph range. Strong easterly winds are creating about 20 knots of wind shear over the wave, which is marginally conducive for development. The disturbance is about 300 miles south of the Saharan Air Layer (SAL), so dust and dry air should not hinder development over the next few days.

Given the disturbance's current lack of organization, combined with the presence of 20 knots of wind shear, any development should be slow to occur. The forecast wind shear along the storm's path over the next five days is predicted to remain at or below 20 knots, which should allow some slow development. Sea surface temperatures (SSTs) will warm from about 28°C to 29°C as the storm progresses westward. The GFS model has been indicating some development is possible in several of its runs over the past few days, but has not been consistent with this prediction. None of the other models show any development of the system. NHC is giving the disturbance a low (less than 30% chance) of developing into a tropical depression over the next two days, which is a good forecast. The GFS and ECMWF models predict the system will be approaching the northern Lesser Antilles Islands by Sunday. Both models forecast the development of a band of very high wind shear just to the north of the islands at that time, so the long-range survival of anything that might manage to develop is in doubt.

CSU forecast team continues to predict an average hurricane season
A near-average Atlantic hurricane season is on tap for 2009, according to the seasonal hurricane forecast issued August 4 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 10 named storms, 4 hurricanes, and 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 83% of average. Between 1950 - 2000, the average season had 10 named storms, 6 hurricanes, and 2 intense hurricanes. But since 1995, the beginning of an active hurricane period in the Atlantic, we've averaged 15 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast is a step down from their June forecast, which called for 11 named storms, 5 hurricanes, and 2 intense hurricanes. Their April forecast called for 12 named storms, 6 hurricanes, and 2 intense hurricanes. The new forecast calls for a near-average chance of a major hurricane hitting the U.S., both along the East Coast (27% chance, 31% chance is average) and the Gulf Coast (26% chance, 30% chance is average). The Caribbean is also forecast to have an average risk of a major hurricane (37%; 42% is average).

The forecasters noted that while sea surface temperature anomalies have increased in the tropical Atlantic and surface pressures have fallen in recent weeks, which normally would favor higher hurricane activity, the presence of El Niño conditions in the Eastern Pacific should counteract these influences. They forecast that the current weak El Niño event will strengthen to a moderate event by September:

El Niño events tend to be associated with increased levels of vertical wind shear and decreased levels of Atlantic hurricane activity. Tropical Atlantic sea surface temperatures anomalies have warmed somewhat since our early June prediction and surface pressures have fallen somewhat. But, the negative influences of El Niño-induced strong Caribbean Basin and Main Development Region vertical wind shear typically dominate over surface pressure and sea surface temperature in the tropical Atlantic.



Figure 1. Change in Sea Surface Temperature anomaly (in °C) between July 2009 and May 2009. Most of the tropical Atlantic has warmed, relative to normal, over the past 2 months. Image credit: NOAA/ESRL.

Analogue years
The CSU team picked four previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: weak to moderate El Niño conditions, and average tropical Atlantic and far northern Atlantic SSTs. Those four years were 2002, which featured Hurricane Lili that hit Louisiana as a Category 1 storm; 1965, which had Category 3 Betsy that hit New Orleans; 1963, which had Category 4 Hurricane Flora that devastated Cuba; and 1957, which didn't have any hurricanes that hit hit land during the peak part of hurricane season. The mean activity for these four years was 9 named storms, 4 hurricanes, and 2 intense hurricanes--almost the same as the 2009 CSU forecast.

How accurate are the August forecasts?
The August forecasts by the CSU team have historically offered a skill of 45 -62% higher than a "no-skill" forecast using climatology (Figure 2). However, they are using a new forecast scheme this year, so it is difficult to judge how skillful this year's forecast might be.


Figure 2. Accuracy of long-range forecasts of Atlantic hurricane season activity performed at Colorado State University (CSU) by Dr. Bill Gray's team (colored squares) and Tropical Storm Risk, Inc. (TSR, colored lines). The skill is measured by the Mean Square Skill Score (MSSS), which looks at the error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TS=Tropical Storms, H=Hurricanes, IH=Intense Hurricanes, ACE=Accumulated Cyclone Energy, NTC=Net Tropical Cyclone Activity. Image credit: TSR.

August 2009 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) also issued a new forecast today, and have increased their numbers by 20% from their June and July forecasts. TSR is also calling for a near-average season, predicting 12.6 named storms, 6.5 hurricanes, 2.8 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 103% of average. Their June forecast called for 10.9 named storms, 5.2 hurricanes, 2.2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 72% of average. The storm numbers are slightly above the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TSR predicts a 40% chance of an above-average season, 44% chance of a near-average season, and a 19% chance of a below-average season, as defined by ACE index. TSR rates their skill level as 51% above chance at forecasting the number of named storms, 60% skill for hurricanes, and 44% skill for intense hurricanes. These are far higher skill numbers than the June ones: 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.8 named storms will hit the U.S., with 1.6 of these being hurricanes. The averages from the 1950-2008 climatology are 3.2 named storms and 1.5 hurricanes. Their skill in making these August forecasts for U.S. landfalls is 25% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.1 named storms, 0.5 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites one main factor for their increased forecast: higher sea surface temperatures than expected over the tropical Atlantic, due to the fact that the trade winds over the Atlantic should be slower than originally anticipated. Faster than average trade winds create less spin for developing storms, and allow the oceans to cool down, due to increased mixing of cold water from the depths and enhanced evaporational cooling.

The CSU and TSR groups are done making forecasts for the coming hurricane season, but NOAA is still due to put out an August update.

I'll have an update on Wednesday.
Jeff Masters

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Yeah,I'm beginning to think this wave aint gonna develop into anything. I'd be surprised if we got development by mid-August.
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Quoting BurnedAfterPosting:
Yellow Circle is gone now

oh well lol, now we dont have to monitor it every second

time for bed

In the morning there will be some uproar.
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Yellow Circle is gone now

oh well lol, now we dont have to monitor it every second

time for bed
Me and my new rototiller are still waiting for the storms.
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Quoting stormsurge39:
When i look at this wave on the satt, it looks a very good cylonic swirl with no (Clothes). When it good convection around it again, i dont think it will have any problem developing into ANA.

It has good vorticity and IMO I agree that it needs some convection to organize further.
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Quoting FloridaTigers:
So when Felicia crosses into the CPAC, will its' name change?


The name is name when was created, so still Felicia.
Member Since: July 21, 2009 Posts: 0 Comments: 552
So when Felicia crosses into the CPAC, will its' name change?
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Member Since: July 21, 2009 Posts: 0 Comments: 552
When i look at this wave on the satt, it looks a very good cylonic swirl with no (Clothes). When it good convection around it again, i dont think it will have any problem developing into ANA.
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Quoting stormsurge39:
How far west does this wave have to go, to not be in such dry air?


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How far west does this wave have to go, to not be in such dry air?
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good monind
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I do believe that little pocket of Cuba and decreasing shear near is expanding.


You can go to the CIMSS website and use the time step function and you will see it grow a little bit bigger
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Quoting VAbeachhurricanes:

some divergence


Quoting Elena85Vet:


At 30? How bout' that?


I thought I saw a bit of a wind shift at 30W
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Quoting weatherwatcher12:
Does anyone see anything interesting in the bottom left part of this image.


At 30? How bout' that?
Member Since: August 18, 2008 Posts: 0 Comments: 628
Quoting weatherwatcher12:
Does anyone see anything interesting in the bottom left part of this image.

some divergence
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Does anyone see anything interesting in the bottom left part of this image.
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Quoting GatorWX:


I know, I guess "well south" was a poor choice of words, but south nonetheless. My main point was it's weakened intensity forecasted.


true, but intensity forcasts beyond 3 days are very hard to predict, yesterday they said felcia wouldnt be a hurricane until tomorrow, and its probably gonna be a cat 4. by tomorrow.
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Iniki II...hide the chickens!
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1199. GatorWX
Quoting VAbeachhurricanes:




well the GFS has it going just north, and the NOGAPS is right at it. So its not a sure thing to go south.


I know, I guess "well south" was a poor choice of words, but south nonetheless. My main point was it's weakened intensity forecasted.
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1198. BDAwx
Quoting GatorWX:
At the moment the storm is only forecast to be a ts in the vicinity of Hawaii, 2nd, the track (at this point) is forecast to be well south of Hawaii, and unless there is an immediate threat in the Pacific, this blog mainly focuses on the Alantic basin. Should the storm affect Hawaii with any ferocity and there is still no major activity in the Atlantic, then I would imagine focus will shift towards the cpac. I simply want to clarify why there's not much attention being given to the Pacific.


Ok
but in my opinion all there is to talk about in the Atlantic has been over talked about
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Quoting Elena85Vet:


And that is a must for it's survival beyond 24-48, no?

It pretty much is, and the vorticity at the lower levels around there is pretty good although it is a little bit broad.

700mb:


850mb:
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Quoting GatorWX:
At the moment the storm is only forecast to be a ts in the vicinity of Hawaii, 2nd, the track (at this point) is forecast to be well south of Hawaii, and unless there is an immediate threat in the Pacific, this blog mainly focuses on the Alantic basin. Should the storm affect Hawaii with any ferocity and there is still no major activity in the Atlantic, then I would imagine focus will shift towards the cpac. I simply want to clarify why there's not much attention being given to the Pacific.




well the GFS has it going just north, and the NOGAPS is right at it. So its not a sure thing to go south.
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1195. Skyepony (Mod)
Felicia
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1194. msphar
The difference between Kuaui and the Big Island is significant. One should pick one's island carefully.
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1193. GatorWX
At the moment the storm is only forecast to be a ts in the vicinity of Hawaii, 2nd, the track (at this point) is forecast to be well south of Hawaii, and unless there is an immediate threat in the Pacific, this blog mainly focuses on the Alantic basin. Should the storm affect Hawaii with any ferocity and there is still no major activity in the Atlantic, then I would imagine focus will shift towards the cpac. I simply want to clarify why there's not much attention being given to the Pacific.
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1192. msphar
My Hawaiian interest is at 1000 feet above MSL and 13000 feet below the mountain tops. I think those two mountains will have a significant impact on the wind/rain any storm may bring.
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Quoting weatherwatcher12:

It's not poofed, but it has not developed. It appears to be trying to develop a new center near 12N and 30W


And that is a must for it's survival beyond 24-48, no?
Member Since: August 18, 2008 Posts: 0 Comments: 628
1190. msphar
I'm not sure I can agree with you VA. I have interests in both areas. Its just a judgement call on my part.
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Quoting BurnedAfterPosting:
36-37W, very pronounced turning there

I have a feeling that once the area back by 30W either breaks away or dissipates, the area at 38W will have a better shot to develop.

Its almost like the area at 30W is robbing energy from the area further to its west.

The only problem is mid-level shear
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Quoting GBguy88:


Right, right...Hurricane Iniki was no sweat :)


first of all, mountains just dont stop winds... and second what about storm surge??? not just a wind with a hurricane
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1187. BDAwx
Quoting GBguy88:


Right, right...Hurricane Iniki was no sweat :)


I think that was sarcasm...
like i always say sarcasm doesn't work in text...
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1186. GBguy88
Quoting msphar:
I don't sweat Hawaii. Those two big mountains should deflect any wind that comes their way. Its the nasty CV waves that I worry about.


Right, right...Hurricane Iniki was no sweat :)
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pronounced turning here too...
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1184. BDAwx
Quoting weatherwatcher12:

It is expected to weaken some because of cooler SST's. Some people also think that he track is incorrect so far out.


yes but the point is that its a more immediate threat not because its threatening land right now but because it has formed already unlike the Atlantic AOI..
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36-37W, very pronounced turning there

I have a feeling that once the area back by 30W either breaks away or dissipates, the area at 38W will have a better shot to develop.

Its almost like the area at 30W is robbing energy from the area further to its west.

The little scattering of thingamablobs is entering lower shear. It will look different in the morning. Everything always does!
Sleep well and dream of beautiful places!
As far as credentials go, the good thing is, you don't need them to post on this site. If you want them, go to NHC site. Link
Member Since: July 11, 2006 Posts: 14 Comments: 11163
What I see is two distinct areas now

First area is around 38W looks like it has mid level cyclonic turning and some convection; structure wise it looks decent

Second area is around 32W, this is where the surface reflection was found early, this area looks more disorganized

If this entire area between 30W-38W is treated as one entity, then the fact that it is so broad makes it looks disorganized as a whole.
Quoting GatorWX:


Looks to me shear is on the increase per the map. That's quite a small area you mentioned.

It could be a start. You never know.
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1179. GatorWX
Quoting weatherwatcher12:
Look at the shear tendency near Cuba and Jamaica. Could we be witnessing some shear dropping in the Caribbean?


Looks to me shear is on the increase per the map. That's quite a small area you mentioned.
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Does the NHC mention our wave in the 8:00 pm Tropical weather discussion, coudn't find it?
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Quoting msphar:
I don't sweat Hawaii. Those two big mountains should deflect any wind that comes their way. Its the nasty CV waves that I worry about.


exactly my point....
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Quoting 7544:
local mets just stated that . Chicklits wave could become a td in 24 to 48 hours im on board with her also
There is a bunch of activity between 30 and 40W that could all consolidate, finally, into a depression. It's just a nice, comfy situation for those little blobs, isn't it?! For Pete's sake, relax. Nature will do what nature does best, which is exactly what She feels like doing!
Think of people you know who you'd like to control but they just never do precisely what you had in mind. Think of yourself. You vow you're going to behave a certain way and then don't. That's what the weather is like. We'd like to impose order on it, but it just does what it wants and we have to stand by and watch it. Personally, I think those little blobs are just bobbing around out there mindlessly and eventually, they'll wind up in a configuration that could be torn apart by shear or not. It really doesn't matter, except if you are in the path and need to be prepared. So it's best to err on the side of caution and figure they may be able to get themselves in a configuration to harness that scattered energy. It is energy, after all, we are watching here, right?! Anyway, I meander myself, but that's cuz I'm under lots of pressure! So goodnight...and thanks for the company! BTW, the crow is being prepared as we speak and should be ready in a couple of days.
Member Since: July 11, 2006 Posts: 14 Comments: 11163
Quoting VAbeachhurricanes:
I wonder if people on here forget hawaii is part of the united states... i mean its possible a major hurricane could hit there this weekend and no one seems to care...

It is expected to weaken some because of cooler SST's. Some people also think that he track is incorrect so far out.
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1174. msphar
I don't sweat Hawaii. Those two big mountains should deflect any wind that comes their way. Its the nasty CV waves that I worry about.
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I wonder if people on here forget hawaii is part of the united states... i mean its possible a major hurricane could hit there this weekend and no one seems to care...
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Quoting Relix:


So this is more Northerly that predicted, which means it will probably become a fish storm right?

That depends on when it lifts out of the ITCZ
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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.