Expert forecasts for 2013 N Atlantic season

[cycloneye]

Dr's Knotzbach / Gray April 10th forecast is up at first post. Among the highlights is that there will be above average U.S and Caribbean major hurricane landfalls,the numbers are above the average and the ACE is 165 with net TC activity at 175%. The analogs are=1915,1952, 1966,1996 and 2004.

[hurricanetrack]

18 named storms. Wow. Wonder if this is another 2005 in the making? Of course, I mean only numbers-wise and not the other terrible ramifications of that season. Those ATL SSTs are quite warm and the Gulf, W ATL and elsewhere will be plenty warm by August when it really counts.

As we all like to say, I guess we'll see....

[cycloneye]

For the island of Puerto Rico there is a 50%/26% and 8% that a Tropical Storm/Hurricane or Major Hurricane pass within 50 miles.

[Blown Away]

Wow, could be an epic season based on pre season predictions.

[cycloneye]

Here is Dr Jeff Masters discussion about the April forecast by CSU:

http://www.wunderground.com/blog/JeffMa ... #commentop

After three consecutive years with a remarkable 19 named storms in the Atlantic, expect another Atlantic hurricane season with similar levels of activity in 2013, says the hurricane forecasting team of Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) in their latest seasonal forecast issued April 10. They call for an Atlantic hurricane season with 18 named storms, 9 hurricanes, 4 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 165. The long-term averages for the past 63 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 103. The active hurricane period that began in 1995 has averaged 15 named storms, 8 hurricanes, and 4 major hurricanes. The 2013 forecast calls for an 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 February and March atmospheric and oceanic conditions were selected as "analogue" years that the 2013 hurricane season may resemble: 2004 (which featured seven major hurricanes, including four that hit the U.S.); 1996 (six major hurricanes, including Cat 3 Hurricane Fran that hit North Carolina); 1966 (three major hurricanes, featuring Cat 4 Inez, which hit Mexico, Hispaniola, Cuba, the Bahamas, and Florida); 1952 (only seven named storms, but three major hurricanes); and 1915, which boasted a Cat 3 hurricane that hit New Orleans and a Cat 4 that hit Galveston. These years all had neutral El Niño conditions, above-average Sea Surface Temperatures (SSTs) in the tropical and North Atlantic, and cool ocean temperatures in the Northeast Pacific (a negative PDO) during February - March. None of the five analogue years had a significant El Niño during the peak of the hurricane season. The average activity for these years was 10 named storms, 7 hurricanes, and 4 major hurricanes.


Figure 1. Hurricane Michael as seen by NASA's Aqua satellite at 12:20 pm EDT Thursday September 6, 2012. At the time, Michael was a major Category 3 hurricane with 115 mph winds. Hurricane Sandy was the only other major Atlantic hurricane of 2012. Image credit: NASA.

Why the forecast of an active season?
The CSU team cited two main reasons why this may be an active hurricane season:

1) Neutral El Niño conditions are expected during the August - September - October peak of hurricane season. Since the active hurricane period we are in began in 1995, neutral years have seen much above-average activity (remember the neutral El Niño year of 2005?) If El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart.

2) Sea surface temperatures (SSTs) in the Main Development Region (MDR) for hurricanes from the Caribbean to the coast of Africa between 10°N and 20°N were near-average in the western tropical Atlantic, but unusually warm in the eastern tropical Atlantic, in March 2013. Much of this unusual warming was due to a persistent negative phase of the North Atlantic Oscillation (NAO) since mid-February (which also brought an unusually cold March to the Eastern U.S. and Western Europe.) A negative phase of the NAO is associated with a weakened Bermuda-Azores High and slower trade winds across the tropical Atlantic. The slower winds allow the ocean to heat up more, due to less mixing of cool water to the surface. Virtually all African tropical waves originate in the MDR, and these tropical waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely.



Figure 2. Departure of sea surface temperature (SST) from average for April 8, 2013, as computed by NOAA's NESDIS branch. SSTs in the hurricane Main Development Region between Africa and Central America (red box) were well above-average.

How good are the April forecasts?
The forecasters are using a statistical model developed in 2011 for making April forecasts, so we don't have a long enough track record to judge how good the new model is. The new model predicted a below-average year for 2012, with 10 named storms, 4 hurricanes, and 2 intense hurricanes. The actual tally was much higher, with 19 named storms, 10 hurricanes, and 2 intense hurricanes. April forecasts of hurricane season activity are low-skill, since they must deal with the so-called "predictability barrier." April is the time of year when the El Niño/La Niña phenomenon commonly undergoes a rapid change from one state to another, making it difficult to predict whether we will have El Niño, La Niña, or neutral conditions in place for the coming hurricane season. Correctly predicting this is key, since if El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart. Currently, ocean temperatures are very close to average in the Eastern Pacific, and the large majority of the El Niño models are predicting a continuation of these neutral conditions for the coming hurricane season.

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 on Monday, June 3, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years.

[beoumont]

CSU seasonal forecasts for many years did not include landfall probabilities. In fact, their outlooks repeatedly noted:

Moreover, these forecasts do not explicitly predict specifically where within the Atlantic basin storms will strike. Landfall probability estimates for any one location along the coast are very low and reflect the fact that in any one season, most US coastal areas will not feel the effects of a hurricane no matter how active an individual season is. And, it must be emphasized that a low probability does not insure that a hurricane will not come ashore.

A few years ago they started adding landfall probabilities for general stretches of coastline; "coincidentally" the same year their research funding started being backed mostly by insurance company concerns. (I am NOT saying CSU fudges their numbers because of this; they simply just started coming up with the best numbers they felt they could.)

This years landfall probabilities are basically this:

First they establish a total number a storms "expected" for the coming year.
Second they compare this number to the average number per year over the course of the base years. In this years case that figure is 150% (18 this year compared to 12 in an average year.)

If you notice the landfall probabilities for each stretch of coastline, they all are within a couple of % points of being 150% of normal for that stretch of coastline - the same ratio of normal total storms compared to this years predicted number.

I would assume they use some "complicated" formula using other statistical studies to come up with these landfall probabilities; but I am fairly certain there is a heavy weight put on inductive reasoning when developing said formula.

Hence, these landfall "probabilities" are mostly just for those concerns that feel they need NUMBERS to back up their business interests: they are not scientifically viable (as CSU again notes.), and weren't meant to be.

[CrazyC83]

The numbers seem reasonable. The SST map looks like a REVERSE of 2012...so more MDR storms, and more Gulf and Caribbean threats?

[Riptide]

The numbers seem reasonable. The SST map looks like a REVERSE of 2012...so more MDR storms, and more Gulf and Caribbean threats?

The tropical cyclone tracks seem to be more dependent on upper-level features rather than sea surface temperatures. If there is another -NAO this summer, Florida and East Coast would be under the gun once again. However, unlike last year....more storms could form in the carribean and gulf rather than moving into the basin if the instability and warm water is available.

[Hurricaneman]

The most commonly used analog years that these experts are using are 2004 and 2005 and during both years Florida and the northern gulf were used for hurricane target practice, I sure hope that doesn't happen and do hope the hurricanes go harmlessly out to sea or we continue the pattern of low instability to save these areas from a real BIG problem

[cycloneye]

For me and the Caribbean friends who live in hurricane alley we can hope for a quiet season.

[CrazyC83]

The most commonly used analog years that these experts are using are 2004 and 2005 and during both years Florida and the northern gulf were used for hurricane target practice, I sure hope that doesn't happen and do hope the hurricanes go harmlessly out to sea or we continue the pattern of low instability to save these areas from a real BIG problem

Considering Florida has gone 7 straight years without a hurricane hit (or significant impact), hurricane amnesia might be settling in...is that 7 year stretch a record?

[Gustywind]

For the island of Puerto Rico there is a 50%/26% and 8% that a Tropical Storm/Hurricane or Major Hurricane pass within 50 miles.

.

[Gustywind]

For me and the Caribbean friends who live in hurricane alley we can hope for a quiet season.

you're definitely right on that... already keeping our fingers crossed

[TheStormExpert]

Considering Florida has gone 7 straight years without a hurricane hit (or significant impact), hurricane amnesia might be settling in...is that 7 year stretch a record?

It will be 8 years this October! The long lasting hurricane shield over Florida will in my opinion have to fade off someday.

[WeatherGuesser]

After three consecutive years with a remarkable 19 named storms in the Atlantic, expect another Atlantic hurricane season with similar levels of activity in 2013,

18 named storms. Wow. Wonder if this is another 2005 in the making?

Wow, could be an epic season based on pre season predictions.

Last I checked, 18 was less than 19, so if the predictions hold true it would be a decrease from the last three years and nothing epic or to show any reason to get dramatic or sensationalistic.

Better question is, will even one make a significant US landfall?

[Extratropical94]

After three consecutive years with a remarkable 19 named storms in the Atlantic, expect another Atlantic hurricane season with similar levels of activity in 2013,

18 named storms. Wow. Wonder if this is another 2005 in the making?

Wow, could be an epic season based on pre season predictions.

Last I checked, 18 was less than 19, so if the predictions hold true it would be a decrease from the last three years and nothing epic or to show any reason to get dramatic or sensationalistic.

Better question is, will even one make a significant US landfall?

But lets not forget the previous April forecasts made by CSU were significantly lower than the one this year, so 18 is in fact an increase if you only look at the pre-season forecasts.

[wxman57]

Last I checked, 18 was less than 19, so if the predictions hold true it would be a decrease from the last three years and nothing epic or to show any reason to get dramatic or sensationalistic.

Better question is, will even one make a significant US landfall?

Yes, 18 is less than 19. But most of last year's 19 storms formed in the Subtropical Atlantic well out to sea, and 3-4 of them were quite weak and short-lived. There were only two hurricanes which barely made Cat 3 strength. In 2004, there were ONLY 15 named storms. 15 is less than 19, too, but that doesn't mean less impact. It all depends on where they form and where they strike.

[NDG]

After three consecutive years with a remarkable 19 named storms in the Atlantic, expect another Atlantic hurricane season with similar levels of activity in 2013,

18 named storms. Wow. Wonder if this is another 2005 in the making?

Wow, could be an epic season based on pre season predictions.

Last I checked, 18 was less than 19, so if the predictions hold true it would be a decrease from the last three years and nothing epic or to show any reason to get dramatic or sensationalistic.

Better question is, will even one make a significant US landfall?

But lets not forget the previous April forecasts made by CSU were significantly lower than the one this year, so 18 is in fact an increase if you only look at the pre-season forecasts.

I think a lot of are making a big deal about CSU's early April forecast because they are usually conservative with numbers, just like in April of 2004 & 2005, 2010, etc
So if conditions stay the same as they are right now across the Atlantic and ENSO regions we could even see a higher number of storms, IMO.

[ROCK]

I think analog years should be used for numbers only and not so much landfall probabilities or speculation.....jmo...

my work region has changed so I hope FL is spared this year though I think it's time for you guys. Just a hunch..

Good to be back on here..

[beoumont]

I think analog years should be used for numbers only and not so much landfall probabilities or speculation.....jmo...

Analog years in the CSU outlook are not used to indicate landfall probabilities; as they distinctly state. From the report:

Analog-Based Predictors for 2013 Hurricane Activity
Certain years in the historical record have global oceanic and atmospheric trends which are similar to 2013 These years also provide useful clues as to likely trends in activity that the forthcoming 2013 hurricane season may bring. For this early April extended range forecast, we determine which of the prior years in our database have distinct trends in key environmental conditions which are similar to current February-March 2013 conditions. Table 6 lists our analog selections.
We select prior hurricane seasons since 1900 which have similar atmospheric-oceanic conditions to those currently being experienced. We searched for years that were generally characterized by neutral ENSO conditions and a negative phase of the Pacific Decadal Oscillation (PDO) during February-March, along with years that had above- average SSTs in the tropical and North Atlantic.
There were five hurricane seasons since 1900 with characteristics most similar ----