Early 2011 Atlantic Hurricane Season Forecasts

By: Dr. Jeff Masters , 6:22 AM GMT on April 07, 2011

Share this Blog
6
+

Hi everybody, this is Dr. Rob Carver filling in for Dr. Masters. 

A continuation of the pattern of much above-average Atlantic hurricane activity we've seen since 1995 is on tap for 2011, according to the latest seasonal forecast issued April 6 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). They are calling for 16 named storms, 9 hurricanes, and 5 intense hurricanes. An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The new forecast is nearly identical to their forecast made in December, which called for 17 named storms, 9 hurricanes, and 5 intense hurricanes. Only six seasons since 1851 have had as many as 17 named storms; 19 seasons have had 9 or more hurricanes. The 2011 forecast calls for a much above-average chance of a major hurricane hitting the U.S., both along the East Coast (48% chance, 31% chance is average) and the Gulf Coast (47% chance, 30% chance is average). The Caribbean is forecast to have a 61% chance of seeing at least one major hurricane (42% is average.) Five years with similar pre-season November atmospheric and oceanic conditions were selected as "analogue" years that the 2011 hurricane season may resemble: 2008, 1999, 1996, 1955, and 2006.  The first four years listed all had neutral to La Niña SST's during hurricane season, while 2006 had El Niño SST's.  The average activity for these years was 12.6 named storms, 7.8 hurricanes, and 4.8 major hurricanes.

This year, the forecasters have introduced a new statistical model for their  April forecasts.  There are four components in this model:

1. Average sea-level pressure in March around the Azores in the subtropical Atlantic.

2. The average of January through March sea-surface temperatures (SST's) in the tropical Atlantic off the coast of Africa.

3. Average sea-level pressure in February and March for the southern tropical Pacific ocean west of South America.

4. Forecasts of September's SST in the tropical Pacific using a dynamical model from the European Centre for Medium-Range Weather Forecasts (ECMWF) 

The first two components are loosely linked together.  Statistical studies have shown that a weaker subtropical high near the Azores, combined with warmer SST's off the coast of Africa in March are associated with weak winds near the surface and aloft from August to October.  This decrease in wind speeds reduces wind shear which can disrupt forming storms.  These March conditions also are associated with warmer SST's in August to October, which is also favorable for more tropical storms.   For this forecast, the first component is strongly favorable for increased hurricane activity, while the second component is weakly negative.

The last two components represent the changes in sea-surface temperature and sea-level pressure that are the El Niño-Southern Oscillation (ENSO).  Briefly speaking,  El Niño conditions (warm sea-surface temperatures) are not favorable for Atlantic hurricanes.  For more info on ENSO and hurricanes, Jeff has this article.

Using the ECMWF model as guidance (see Figure 1), the CSU group believes that SST's in the tropical Pacific will be neutral (less than 0.5°C from normal).  This would have a small negative effect on hurricane activity.  However, the tropical Pacific sea-level pressure shows that the atmosphere looks like a La Niña event is still going on.  This is strongly favorable for Atlantic hurricane activity in the CSU group's model.

Figure 1. Forecasts of El Niño conditions by 20 computer models, made in March 2011. The ECMWF forecast used by the CSU group is represented by the dark orange square.  The forecasts for August-September-October (ASO) show that 5 models predict El Niño conditions, 7 predict neutral conditions, and 5 predict a weak to moderate La Niña. El Niño conditions are defined as occurring when sea surface temperatures in the Equatorial Pacific off the coast of South America ( the "Niño 3.4 region) rise to 0.5°C above average (top red line). La Niña conditions occur when SSTs in this region fall to 0.5°C below average. Image credit: Columbia University.

How accurate are the April forecasts? While the formulas used by CSU do well in making hindcasts--correctly modeling the behavior of past hurricane seasons--their April hurricane season forecasts have had no skill in predicting the future. This year's April forecast is using a new system and has not yet produced a verified forecast.  The scheme used in the past three years successfully predicted active hurricane seasons for 2008 and 2010, but failed to properly predict the relatively quiet 2009 hurricane season. A different formula was used prior to 2008, and the April forecasts using that formula showed no skill over a simple forecast using climatology. CSU maintains an Excel spreadsheet of their forecast errors ( expressed as a mathematical correlation coefficient, where positive means a skilled forecast, and negative means they did worse than climatology) for their their April forecasts. For now, these April forecasts should simply be viewed as an interesting research effort that has the potential to make skillful forecasts. The next CSU forecast, due by June 1, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years.


Figure 2.
Accuracy of long-range forecasts of Atlantic hurricane season activity performed by Phil Klotzbach and Bill Gray of Colorado State University (colored squares) and Tropical Storm Risk, Inc. (colored lines). The CSU team's April forecast skill is not plotted, but is less than zero. 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.

2011 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.

The  British  private  forecasting  firm  Tropical Storm Risk, Inc.  (TSR),   issued  their  2011  Atlantic hurricane season forecast on April 5. They are also calling for  a  very  active  year: 14. 2 named storms, 7.5 hurricanes, and 3.6 intense hurricanes. We would round that to 14 named storms, 8 hurricanes, and 4 intense hurricanes.   This  compares to their forecast issued in December of 15.6 named storms, 8.4 hurricanes,   and intense hurricanes. TSR predicts a 55%  chance  of  an  above-average  hurricane season, 28% chance of a near-normal season, and only a 17%  chance  of  a  below normal season. TSR bases their April forecast on predictions  that  sea  surface temperatures this fall in the tropical  Atlantic  will  be  above  about  0.08°C above average, and trade  wind  speeds  will  be  about 0.2  m/s  slower  than average.  The decrease in the trade wind speeds is favorable for enhanced hurricane activity, while the forecast SST's are expected to be neutral for hurricane activity.

TSR puts their skill level right next to the forecast numbers: 13% skill above chance at forecasting the number of named storms, 11% skill for hurricanes, and 10% skill for intense hurricanes. That's not much skill, and really, we have to wait until the June 1 forecasts by CSU, NOAA, and TSR to get a forecast with reasonable skill.

Rob's critiques of the April forecasts
I have to note that Jeff and I wrote this article together.  He wrote the general framework before the forecasts were issued, while I wrote the details based on the actual forecasts.  So the preceding text is a joint production.  However, I have a few observations to make that are my responsibility alone.

First, I am disappointed that the CSU group has changed forecast models only after three seasonal forecasts.  This makes it very difficult to assess the skill of the current forecast using past performance.  This is very important for forecast users, and they do it everyday.  For example, I tend to discount a forecast of rain if it comes from a source that over-forecasts rain (The boy who cried wolf problem).

In the documentation that came with the April forecast, the CSU group argue that the hindcasts show the new forecast model has skill.  However, I think hindcasts are a poor substitute for real forecasts in understanding the skill of a statistical forecast model, like that of the CSU's group.  As Jeff noted, the previous forecast model did well with the hindcasts and yet had mixed results with the actual forecasts.  This does not give me confidence that the new forecast model will be superior to the previous model.

From a philosophical viewpoint, I am inherently cautious about statistical forecast models like the one used by the CSU group.  Essentially, they look at what happened in the past and use that to predict the future.  However, for making forecasts, we assume that the relationships in space and time between the predictors (such as the average March sea-level pressure around the Azores) and the predictands (Atlantic hurricane activity) does not change as we move forward in time.  In a world with climate change, that's a tricky assumption to make.

In any event, it is customary in the meteorological community to continue running older forecast guidance models after the introduction of newer models.  This allows forecasters and forecast users to leverage their knowledge of the forecast skill of the older model and gain insight into the forecast skill of the new model.  The CSU group really should have included the forecast from the previous statistical forecast system in this forecast.     

I am uneasy with some of the methodology choices made in implementing the forecast model.  Data for the first three predictors was obtained from the Climate Forecast System Reanalysis (CFSR), NOAA's newest and most advanced reanalysis product.  However, CFSR data for 2010 and 2011 has not been released yet, so the CSU group used NCEP/NCAR Reanalysis (NNR), NOAA's first-generation reanalysis, to fill in the gaps.  Due to differences in design, resolution, etc., CFSR and NNR can have different depictions of the state of the atmosphere.  So using NNR's March 2011 average SLP instead of CFSR's could alter the forecast in unexpected ways.  It would be interesting to see how CFSR's 2010-2011 data changes the results. 

In any event, we will have to wait and see what the Atlantic hurricane season of 2011 brings.

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1484 - 1434

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35Blog Index

Quoting twincomanche:
I love you but 'largely' needs to be left out. Most are stirring around statistics for the agriculture department that will be published two years later and the like. It's unfortunate.

No Dear, Ag Dept. bsers are the minority.
Most of the government workers are social workers, teachers, cops and the like who on a daily basis are on the front lines of preserving 'The American Way' despite all odds.
I am a witness and would sign an affidavit in court to this effect.
Member Since: Posts: Comments:
Quoting Levi32:


That's the 2nd time you've said 16. I think you misheard. My current prediction is 14-15.

Didn't hear your prediction, I was going by the official prediction from CSU etc. of 16/9/5. I'm quite surprised your prediction is that low, as you are known around here as one of the more liberal Atl. hurricane forecasters around here.

Do you remember what your prediction was in the spring of 2008? I remember as Drak and hurricane23 predicted below average seasons for that year.

One question -- what made that certain El Nino season most unlike the rest of the El Nino seasons? It was borderline moderate, not an extremely weak El Nino like in some years.
Member Since: Posts: Comments:

Quoting Chicklit:
holey patootie mrstormx.
it does look directed toward greenbay.
Ya its kind of surprising, that region of Wisconsin doesn't see that many tornadoes. I think Brown county has had something like 22 total tornadoes recorded since 1950, so to think these cells are heading that direction is somewhat scary.
Member Since: Posts: Comments:
1480. Patrap
NEXRAD Radar
Green Bay, Vertically Integrated Liquid Range 124 NMI

Member Since: Posts: Comments:
1478. Patrap
NEXRAD Radar
Green Bay, Base Reflectivity 0.50 Degree Elevation Range 124 NMI

Member Since: Posts: Comments:
1477. Levi32
Quoting altesticstorm011:

Not a good deal lower.

19-16 = 3 so that's not really much of a big difference. And based on SSTs being higher this year than 2008 I think this year should be more active than 2008, which otherwise is the best analog year (Why the heck did they pick 2006? That was an El Nino). 17 or 18 storms is feasible which is barely less than last year.


That's the 2nd time you've said 16. I think you misheard. My current prediction is 14-15.
Member Since: Posts: Comments:
holey patootie mrstormx.
it does look directed toward greenbay.
Member Since: Posts: Comments:
NOAA Weather radio just went off (1900 Hours) with a Severe Thunderstorm Watch for Tarrant, Ellis, Jack, Parker, Palo Pinto, Johnson and Bosque Counties until 0200 Hours CST. The extreme southern end of the front is now seeing storm development about 60 miles or so to the NNW of Fort Worth. Also, "Weather Dog" my 8-year old Black Lab was not two feet away from my wife and I during dinner during the last 45 minutes; had to bribe her with T-Bone so she would go outside....the Lab gets very concerned over approaching low pressure systems and her actions are a really good way to judge how bad things are going to be.....anyway, my first post since last October at the conclusion of Hurricane Season....the next 45 days are traditionally the really dangerous ones for the DFW Metroplex with regards to severe weather.
Member Since: Posts: Comments:
1474. Levi32
Quoting altesticstorm011:

That's right. Normal. That's all it was. Normal. Nothing special until September when the excitement and thrill of a hurricane season full of potential is over. Even in a certain El Nino year in the last ten years there were 8 storms including 3 major hurricanes in the month of August.


7 storms and 2 majors, and that was a different El Nino year than most.

One can't put too much weight on what happens in the early season. El Nino years actually tend to have early starts, but it is the core of the season that matters most, and one can't forget that 2010 was tied for the 2nd most active season in terms of named storms since 1950.
Member Since: Posts: Comments:
Quoting Levi32:


During the winter the positive NAO does tend to reduce SSTs, as it has been slowly doing recently, but during the summer it is much more variable, as the trade wind belt has the flexibility to shift meridionally.

As far as landfalling storms, it does seem likely that there will be more threat for that this year than last year, though overall storm number should be a good deal lower.

Not a good deal lower.

19-16 = 3 so that's not really much of a big difference. And based on SSTs being higher this year than 2008 I think this year should be more active than 2008, which otherwise is the best analog year (Why the heck did they pick 2006? That was an El Nino). 17 or 18 storms is feasible which is barely less than last year.
Member Since: Posts: Comments:
This big monster is heading towards the fox cities and Green Bay, a large tornado through there would probably prompt a tornado emergency.


Member Since: Posts: Comments:
Thanks for the links emcf.
People need to be reminded of the importance of timely and adequate public services.
For some reason there is an "anti-government" sentiment, with people not realizing that "government" consists primarily of people looking out for public health and safety.
"Legislators" are another category altogether.
Member Since: Posts: Comments:
Avalanche Risk: Monitoring System Warns of Slippery Slopes

ScienceDaily (Apr. 10, 2011) — As a consequence of climatic changes, the number of avalanche threats has been increasing in the Alps and other alpine regions, with fatal consequences for people and infrastructures. Continuous monitoring of every endangered area has been lacking until now due to high costs and manpower requirements. Geological researchers in Munich have now developed an inexpensive system, which with the help of several technologies can continuously monitor slopes, assess changes, and provide early warnings to communities potentially affected by landslides.

Link
Member Since: August 2, 2010 Posts: 21 Comments: 9814
Quoting Levi32:


I don't think it was delayed. There is a climatological average of 1 named storm before August 1st, and we had 2 plus a depression. We went for two weeks in July with no activity and that was about it. It took us until mid-August to start cranking out the major storms, which is normal.

That's right. Normal. That's all it was. Normal. Nothing special until September when the excitement and thrill of a hurricane season full of potential is over. Even in a certain El Nino year in the last ten years there were 8 storms including 3 major hurricanes in the month of August.
Member Since: Posts: Comments:
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
647 PM CDT SUN APR 10 2011

ILZ015-016-024-110015-
HENRY-MERCER-ROCK ISLAND-
647 PM CDT SUN APR 10 2011

...STRONG THUNDERSTORM WITH SMALL HAIL AND GUSTY WINDS...

AT 641 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
STRONG THUNDERSTORM NEAR NEW WINDSOR...OR 14 MILES EAST OF ALEDO...
MOVING NORTHEAST AT 55 MPH.

* THE THUNDERSTORM WILL BE NEAR...
6 MILES SOUTHEAST OF ORION AROUND 650 PM CDT...
CAMBRIDGE AROUND 655 PM CDT...
GENESEO AROUND 700 PM CDT...

HAIL UP TO PENNY SIZE AND GUSTY WINDS OF 40 TO 50 MPH CAN BE EXPECTED
WITH THIS STORM.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 100 AM CDT MONDAY MORNING FOR
SOUTHEASTERN IOWA AND NORTHWESTERN ILLINOIS AND NORTHEAST MISSOURI.

LAT...LON 4133 8989 4114 9029 4115 9043 4110 9044
4118 9056 4154 9023
TIME...MOT...LOC 2346Z 226DEG 48KT 4122 9040

$$
Member Since: Posts: Comments:
1467. 7080734
Look's like Neal Wikner might have a funnel.
Member Since: Posts: Comments:
1466. Levi32
Quoting altesticstorm011:

So in your opinion what delayed the hurricane season last year?


I don't think it was delayed. There is a climatological average of 1 named storm before August 1st, and we had 2 plus a depression. We went for two weeks in July with no activity and that was about it. It took us until mid-August to start cranking out the major storms, which is normal.
Member Since: Posts: Comments:
Quoting Levi32:


It's also folly to say there's a lag when the atmosphere itself said otherwise. The atmosphere was behaving like La Nina before the ocean was.

So in your opinion what delayed the hurricane season last year?
Member Since: Posts: Comments:
1463. emcf30
Neal Wikner is going thru a area that looks like it was hit hard
Member Since: Posts: Comments:
1462. 7080734
Neal Wikner has a funnel cloud.
Member Since: Posts: Comments:
1461. Levi32
Quoting altesticstorm011:

........which was pretty much the only entity of note the first two-and-three-fourths months of the hurricane season. It would be folly to deny a lag of some sort when you've got higher SSTs and lower shear than in two seasons earlier in the half-decade which had 7 and 5 storms (2 major hurricanes each) in the months of June and July combined...


It's also folly to say there's a lag when the atmosphere itself said otherwise. The atmosphere was behaving like La Nina before the ocean was.
Member Since: Posts: Comments:
1460. Levi32
Quoting altesticstorm011:

During the winter and the first 70% of spring however the westerlies account for the vast majority of Atlantic wind shear; the NAO, on the other hand, mostly influences trade winds, or easterlies, as well as cooling SSTs when positive.

During the hurricane season the westerlies are dead so most of the wind shear consists of trade winds (influenced by the High, this is especially true for the TATL), entities such as ULLs and TUTTs as well as any coexisting tropical cyclones. If the NAO continues to remain positive the SSTs in the TATL will cool down to average and dry air might also become an issue. If it oscillates the SSTs should be allowed remain above, even increase to well above average and dry air shouldn't be too much of a factor. Either way the Bermuda High should be strong enough to allow for 2011 to be a land storm year -- agree, Levi?


During the winter the positive NAO does tend to reduce SSTs, as it has been slowly doing recently, but during the summer it is much more variable, as the trade wind belt has the flexibility to shift meridionally.

As far as landfalling storms, it does seem likely that there will be more threat for that this year than last year, though overall storm number should be a good deal lower.
Member Since: Posts: Comments:
Quoting Levi32:


Don't forget that we generally measure atmospheric lag by looking at the SOI, and by that measure, the atmosphere was already into La Nina conditions by the time May came around, actually 2 months ahead of the sea surface temperatures. There was no atmospheric lag last year. We also had a Cat 2 hurricane in June.


........which was pretty much the only entity of note the first two-and-three-fourths months of the hurricane season. It would be folly to deny a lag of some sort when you've got higher SSTs and lower shear than in two seasons earlier in the half-decade which had 7 and 5 storms (2 major hurricanes each) in the months of June and July combined...
Member Since: Posts: Comments:
Quoting Levi32:


That's not always true either. For example, during the winter, Caribbean and tropical Atlantic wind shear plummeted far below normal as soon as the AO finally reversed to positive in mid-late January.

The numerical value of the AO/NAO does not fully describe the long-wave pattern in the northern hemisphere. This is especially true in the summer, and is the reason why solid conclusions can't be drawn by just looking at the sign of the indices. They do not always result in the same things.

During the winter and the first 70% of spring however the westerlies account for the vast majority of Atlantic wind shear; the NAO, on the other hand, mostly influences trade winds, or easterlies, as well as cooling SSTs when positive.

During the hurricane season the westerlies are dead so most of the wind shear consists of trade winds (influenced by the High, this is especially true for the TATL), entities such as ULLs and TUTTs as well as any coexisting tropical cyclones. If the NAO continues to remain positive the SSTs in the TATL will cool down to average and dry air might also become an issue. If it oscillates the SSTs should be allowed remain above, even increase to well above average and dry air shouldn't be too much of a factor. Either way the Bermuda High should be strong enough to allow for 2011 to be a land storm year -- agree, Levi?
Member Since: Posts: Comments:
1457. emcf30
href="http://http://www.radioreference.com/apps/au dio/?ctid=3061" target="_blank">Link

Interesting audio of emergency services of the tornado touchdown. Seems like massive damage. Roads are impassable in the area.

Link
Member Since: Posts: Comments:
1456. 7080734
Looks like SWIFT's got something.
Member Since: Posts: Comments:
1454. emcf30
Lot of damage in the Cottondale, Adams area. Dispatch receiving multiple calls, Listing to law enforcement reporting Tornado is on the ground in that area. They are reporting now there are houses totally missing
Member Since: Posts: Comments:
1453. Levi32
Quoting altesticstorm011:
It's hard to tell (as last year hypists were saying the same thing, that the season was a month ahead of schedule and there will be storms forming in May [yada yada] when in fact the season was three months behind schedule due to the rapid El Nino---->La Nina transition), however without any radical changes likely to occur with the ENSO this year as it shifts to neutral but not El Nino, it seems that there will be no atmospheric lag this time around to stall this hurricane season.


Don't forget that we generally measure atmospheric lag by looking at the SOI, and by that measure, the atmosphere was already into La Nina conditions by the time May came around, actually 2 months ahead of the sea surface temperatures. There was no atmospheric lag last year. We also had a Cat 2 hurricane in June.

Member Since: Posts: Comments:
1452. KEEPEROFTHEGATE (Mod)
LETS LIGHT IT UP

Member Since: Posts: Comments:
1451. Levi32
Quoting altesticstorm011:
I think the guy's got it mixed up.

+ NAO = stronger Bermuda High = stronger trade winds = more shear, westerly track influence
- NAO = weaker Bermuda High = weaker trade winds = less shear, north and westerly track influence

However, keep in mind that 10 knots of shear below average in the Caribbean on April 25 is still too high for a storm to form. On May 25 it might be a different story, however.


That's not always true either. For example, during the winter, Caribbean and tropical Atlantic wind shear plummeted far below normal as soon as the AO finally reversed to positive in mid-late January.

The numerical value of the AO/NAO does not fully describe the long-wave pattern in the northern hemisphere. This is especially true in the summer, and is the reason why solid conclusions can't be drawn by just looking at the sign of the indices. They do not always result in the same things.
Member Since: Posts: Comments:
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
554 PM CDT SUN APR 10 2011

IAZ067-068-078-ILZ015-024-102330-
LOUISA-MERCER-MUSCATINE-ROCK ISLAND-SCOTT-
554 PM CDT SUN APR 10 2011

...SMALL HAIL AND GUSTY WINDS...

AT 552 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED AN
AREA OF STRONG THUNDERSTORMS 7 MILES WEST OF MANNON...OR NEAR
WAPELLO...MOVING NORTHEAST AT 40 MPH.

* THE THUNDERSTORM WILL BE NEAR...
MANNON AROUND 600 PM CDT...
ELIZA AROUND 605 PM CDT...
ILLINOIS CITY AROUND 615 PM CDT...
FAIRPORT AND 9 MILES NORTHWEST OF HAMLET AROUND 620 PM CDT...
MONTPELIER AROUND 625 PM CDT...
ANDALUSIA AND 8 MILES NORTHWEST OF TAYLOR RIDGE AROUND 630 PM
CDT...

HAIL UP TO PENNY SIZE...GUSTY WINDS OF 40 TO 50 MPH AND BRIEF HEAVY
RAIN CAN BE EXPECTED WITH THESE STORMS.

LAT...LON 4153 9086 4137 9059 4114 9110 4125 9119
TIME...MOT...LOC 2253Z 225DEG 35KT 4123 9109

$$
Member Since: Posts: Comments:
Tornado watch in IL now also
Member Since: Posts: Comments:
1448. Levi32
Quoting alfabob:


So basically even if the arctic air mass begins to spill out, wind shear is still going to be below normal in the Caribbean? I know that the AO/NAO isn't the only influential aspects, but they should be some of the key ingredients in overall shear. The SST anomalies combined with the arctic dipole and sea ice volume (ocean-atmospheric coupling) are probably becoming more influential than usual. Maybe it is possible to get a TD or TS in May then (if the season is really a month ahead of schedule, this would be basically June).


It's impossible to know if we will see anything in the way of tropical activity during May. All we can look at right now are conditions that could foreshadow the early season setup.
Member Since: Posts: Comments:
Quoting KoritheMan:
The westerlies are always in control this time of year. I'm not concerned until the final week of May.

Yes.

See 1444.
Member Since: Posts: Comments:
It's hard to tell (as last year hypists were saying the same thing, that the season was a month ahead of schedule and there will be storms forming in May [yada yada] when in fact the season was three months behind schedule due to the rapid El Nino---->La Nina transition), however without any radical changes likely to occur with the ENSO this year as it shifts to neutral but not El Nino, it seems that there will be no atmospheric lag this time around to stall this hurricane season.
Member Since: Posts: Comments:
The westerlies are always in control this time of year. I'm not concerned until the final week of May.
Member Since: Posts: Comments:
Quoting Levi32:


Not necessarily. The influence on wind shear in the Atlantic is not a fixed mode of variability associated with the AO/NAO.

While the GFS is predicting the AO to go back towards negative by day 15, it also keeps 250mb westerly winds about 10 knots below normal in the western Caribbean at that same time.

I think the guy's got it mixed up.

+ NAO = stronger Bermuda High = stronger trade winds = more shear, westerly track influence
- NAO = weaker Bermuda High = weaker trade winds = less shear, north and westerly track influence

However, keep in mind that 10 knots of shear below average in the Caribbean on April 25 is still too high for a storm to form. On May 25 it might be a different story, however.
Member Since: Posts: Comments:
1443. 7080734
Funnel reported near SWIFT.
Member Since: Posts: Comments:
levi32...If that stands to be right,could it increase the number of storms we have this year?
Member Since: Posts: Comments:
Brandon Sullivan has a nice wall cloud
Member Since: Posts: Comments:
1439. Patrap
Quoting MrstormX:
MIDSCAR-HARV 2 looks like a tornado on cam, I saw a tranformer just blow...


Roger dat,...itsa bad scene up dat way
Member Since: Posts: Comments:
Quoting Levi32:


That's because of where the average battle-zone between warm and cold is in April during moderate-strong La Ninas. It would seem like that is pretty normal.



that makes sense
Member Since: August 21, 2008 Posts: 0 Comments: 7441
1437. KEEPEROFTHEGATE (Mod)
Member Since: Posts: Comments:
1436. Levi32
Quoting alfabob:
Well I was thinking if AO stayed positive then a possible TS could form around the Caribbean; but shear should be increasing soon (AO is going negative), so it most likely won't happen. The top image is from a couple of days ago when AO was positive; but due to the build-up of heat, arctic air is being displaced.




Not necessarily. The influence on wind shear in the Atlantic is not a fixed mode of variability associated with the AO/NAO.

While the GFS is predicting the AO to go back towards negative by day 15, it also keeps 250mb westerly winds about 10 knots below normal in the western Caribbean at that same time.

Member Since: Posts: Comments:
But now he is moving so idk
Member Since: Posts: Comments:

Viewing: 1484 - 1434

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35Blog Index

Top of Page

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.

Local Weather

Partly Cloudy
74 °F
Partly Cloudy