The failure of preseason predictions for the hurricane season of 2006

By: Dr. Jeff Masters , 2:05 PM GMT on December 12, 2006

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The preseason predictions of an extremely active hurricane season were spectacularly wrong. Only nine named storms and five hurricanes formed in the Atlantic, one below the average of ten named storms and six hurricanes. We ended up with the quietest hurricane season since 1997, much to the relief of regions ravaged by the unprecedented activity of 2004 and 2005. What happened to make the prognostications such a abysmal failure?



Dry air and dust
A significant reason for the failure appears to be the unusual amount of dry air laden with African dust that came off the Sahara Desert during July and August. Hurricanes need moist air at mid-levels of the atmosphere in order to form, and recent research suggests that the dust within the dry air may act as an inhibiting factor as well, through some not well-understood process. In addition, these dry air outbreaks are frequently accompanied by a strong jet of easterly winds that brings hostile wind shear over the Atlantic. As seen in a plot of the relative humidity at 500 mb (roughly 18,000 feet altitude) in August of 2006 (Figure 1), there was much drier air than usual over a large portion of the tropical Atlantic where hurricanes like to form.

Why was there so much dry air and dust? During the early part of the rainy season (May-July) in the southern Sahel region of Africa, precipitation was well below average (Figure 2). Rainfall was also below average in this region in 2005, and these factors could have contributed to more Saharan dust being blown out over the tropical Atlantic in 2006.

Figure 1. Departure from normal of relative humidity for the month of August, at 500 mb (about 18,000 feet altitude).

Figure 2.Departure of precipitation from normal for May-July 2006 for Africa. Note that the southern Sahel region (approximately 10-15ºN, 0-15ºW) had much below average precipitation, and this likely contributed to the dry air and widespread Saharan dust outbreaks observed over the tropical Atlantic this year. Image credit: Bill Gray and Phil Klotzbach's Summary of 2006 Atlantic Tropical Cyclone Activity and Verification of Author's Seasonal and Monthly Forecasts at Colorado State University.

El Niño
The other reason the hurricane season of 2006 was so mild is probably due to the arrival of El Niño conditions in September. It is well known that when the warming of the Equatorial Pacific waters off the coast of South America brings about an El Niño event, the number and intensity of Atlantic hurricanes is sharply reduced. Conversely, action in the Eastern Pacific is enhanced, and we saw both of these effects in 2006. The reason usually given for this lack of activity in the Atlantic is an increase in wind shear. The warm waters of the eastern Pacific lead to more rising air than usual there, and when that rising air hits the top of the troposphere (the lower atmosphere), it spreads out and creates strong upper-level winds that blow from east to west towards the Western Pacific, and west to east over the Atlantic. These strong upper-level winds create hostile wind shear that tears apart developing hurricanes. However, in 2006, it appears that El Niño-induced wind shear was not a serious impediment to Atlantic hurricane formation. Wind shear was near average over the Atlantic during most of hurricane season (Figure 3). There are additional reasons El Niño suppresses hurricane activity, and foremost among these is the introduction of stable, sinking air over the Atlantic. It is likely that El Niño brought such conditions to the Atlantic during large portions of the 2006 hurricane season, significantly inhibiting hurricane formation.


Figure 3. Wind shear over the tropical Atlantic. Except for a big above-normal spike in October, wind shear in 2006 (blue line) was near normal (black line) over the tropical Atlantic during hurricane season. Image credit: NOAA/CIRA.

So why did the long range forecasts fail?
The long range seasonal hurricane predictions are statistical in nature--they look for early season patterns in winds, pressures, and ocean temperatures that occurred in years past that one can combine to make a skillful prediction of the hurricane season. One of the variables these prediction schemes typically do not include is the early season rainfall in Africa. If it is an unusually dry and dusty year over the Atlantic like 2006 was, then the forecast is going to be wrong. The other problem was the unusual nature of the El Niño event that developed this year. We went from La Nina conditions in March to a full-fledged El Niño in September. This was by far the largest percentage warming of SST anomalies between June-July and August-September in the tropical Pacific for a year that had El Niño conditions in August-September. In addition, the the timing was unusual--it is uncommon for El Niño events to start in the Fall. Since the historical record had very few cases mimicking the behavior of this year's El Niño event, it is no wonder that the statistical models which rely on past years' data to come up with forecasts of hurricane activity failed. El Niño behaved too strangely this year to anticipate, and the computer models had no idea it was coming until about March or April.

Jeff Masters

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195. ProgressivePulse
4:14 PM GMT on December 14, 2006
ANOTHER good radar view showing the convergence.
Member Since: August 19, 2005 Posts: 5 Comments: 5396
194. Skyepony (Mod)
3:45 PM GMT on December 14, 2006
Oh good, you crushed your own hopes, I was about to point out that shear...

Still got a long shot, outside chance of a freak, late season one over the Azores, nogaps, gfs, cmc (phase anylisis). The models have actually been leaning more toward it as the event approaches.
Member Since: August 10, 2005 Posts: 162 Comments: 37829
193. cajunkid
3:43 PM GMT on December 14, 2006
WU model maps
Member Since: July 10, 2005 Posts: 3 Comments: 1279
192. hurricane23
3:39 PM GMT on December 14, 2006
weatherboychris visit my website and go threw the navagation bar and click on tropical sites or if not click on radar.

Adrian's weather

Member Since: May 14, 2006 Posts: 8 Comments: 13786
191. hurricane23
3:37 PM GMT on December 14, 2006
Rainshowers seem to be coming up from the south and converging over south florida.


Member Since: May 14, 2006 Posts: 8 Comments: 13786
190. weatherboykris
3:36 PM GMT on December 14, 2006
What site are you using?
Member Since: December 9, 2006 Posts: 125 Comments: 11346
189. weatherboykris
3:36 PM GMT on December 14, 2006
No problems here.
Link
Member Since: December 9, 2006 Posts: 125 Comments: 11346
188. hurricane23
3:26 PM GMT on December 14, 2006
Here is a large view of the GOM...You can somewhat make out some cyclonic spin in the clouds.

24 FRAME VISIBLE LOOP OF THE GOM
Member Since: May 14, 2006 Posts: 8 Comments: 13786
187. cajunkid
3:21 PM GMT on December 14, 2006
anyone have problems when they try to pull up the gfs model map for Canada? All I get is a little box with an X in it.
Member Since: July 10, 2005 Posts: 3 Comments: 1279
186. weatherboykris
3:21 PM GMT on December 14, 2006
And then just when I get my hopes up,the shear map crushes them
Member Since: December 9, 2006 Posts: 125 Comments: 11346
185. weatherboykris
3:14 PM GMT on December 14, 2006
Link
Water temps still 80F at this buoy,which is even further north of the wave...
Member Since: December 9, 2006 Posts: 125 Comments: 11346
184. hurricane23
3:14 PM GMT on December 14, 2006
Overall alot of rain over southflorida for the next 24-36 hours.If a surface low were indeed to form it will be weak and will amount to much needed rain for south florida.

RADAR
Member Since: May 14, 2006 Posts: 8 Comments: 13786
183. MisterPerfect
3:10 PM GMT on December 14, 2006
Much needed rain for south florida...Expected to get heavier towards late afternoon into the night time hours.

...great!
Member Since: November 1, 2006 Posts: 71 Comments: 20137
182. weatherboykris
3:09 PM GMT on December 14, 2006
It appears as though it is still an open wave, although the morning Quickscat missed most of the area.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
181. ProgressivePulse
3:03 PM GMT on December 14, 2006
HERE is a good radar link w/ visible
Member Since: August 19, 2005 Posts: 5 Comments: 5396
180. Skyepony (Mod)
3:03 PM GMT on December 14, 2006
It's on MLB Radar too. Rained here a good bit of the night.

According to the MLB Local all the models went with an open wave but the gfs.

Patrap~ everyday should begin like that.
Member Since: August 10, 2005 Posts: 162 Comments: 37829
179. hurricane23
3:03 PM GMT on December 14, 2006
Much needed rain for south florida...Expected to get heavier towards late afternoon into the night time hours.

NWS discussion from 3am.

.DISCUSSION...MODELS CONTINUE TO BE IN DISAGREEMENT ABOUT THE WX
FOR S FLA NEXT 48 HOURS. THE GFS SHOWS SHORTWAVE TROUGH CURRENTLY
DIGGING INTO S TX/NORTHERN MEXICO AND THEN DEVELOPING A SFC LOW
OVER THE EASTERN GOFMEX WHILE THE NAM SHOWS NOTHING OF THE KIND.
WATER VAPOR IMAGERY DOES SHOW SUBTROPICAL JET MOVING INTO THE
WESTERN GOFMEX WITH SLIGHT CYCLONIC CURVATURE DEVELOPING SO WILL
LEAN TOWARDS THE GFS SOLUTION. AS THIS THEN TRAVERSES ACROSS THE
FL PENINSULA COULD BE A DECENT RAIN PRODUCER AND WE ARE IN DIRE
NEED OF THAT. THE HEAVIEST RAIN WILL TEND TO OCCUR THURSDAY NIGHT
INTO FRIDAY AS ALL OF THIS INTERACTS OVER S FLA. THE GFS HAD BEEN
SLOWING THE SPEED OF THE LOW DOWN BUT THE 00Z RUN NOW SPEEDS IT UP
AGAIN AND BY FRIDAY EVENING WILL BE EXITING THE SE CST. THIS IN
TURN WILL END OUR PRECIP EARLIER SO HAVE LOWERED THE POPS FOR
FRIDAY NIGHT AND SATURDAY. AS THIS OCCURS STRONG SUBTROPICAL RIDGE
WILL BUILD ACROSS THE GOFMEX AND EXTEND ACROSS FLA AS A LARGE
SHORTWAVE DIGS INTO THE DESERT SW. AS THIS LOW THEN MOVES INTO TX
BY THE MIDDLE OF NEXT WEEK, SOME OF THE MOISTURE COULD GET CAUGHT
BACK UP AND INCREASE OUR POPS AT THAT TIME. FOR NOW, HAVE NOT
CHANGED MUCH OF THE EXTENDED PERIOD.
Member Since: May 14, 2006 Posts: 8 Comments: 13786
178. weatherboykris
2:49 PM GMT on December 14, 2006
Forget satellite loops,its all in range of Cuban radar
Link
Member Since: December 9, 2006 Posts: 125 Comments: 11346
177. pottery
1:24 PM GMT on December 14, 2006
Good morning Patrap and all, it's freezing here man, got gown to 70 last nite. Had to reach for the blanket and turn off the ceiling fan..........
Member Since: October 24, 2005 Posts: 0 Comments: 24307
176. Patrap
12:41 PM GMT on December 14, 2006
Member Since: July 3, 2005 Posts: 424 Comments: 128259
175. WSI
11:38 AM GMT on December 14, 2006
LOL! Having Bastardi's dire statement for the Northeast in there is classic. I remember when he said that. He hyped it so much.
174. TayTay
11:22 AM GMT on December 14, 2006
Intense storm's coming to the Pacific Northwest.
171. Skyepony (Mod)
5:39 AM GMT on December 14, 2006
Kris~ check out the rain rates on Nexsat, take it some clicks back in time. Whats headed toward S FL has decreased from 9.3 to 5.7mm/hr in just the last few hours...where there was nothing headed toward C FL a few hours ago there is rain. S FL may get more rain, but the rest of the peninsula looks to be still in this, sat loop. Right now the coldest tops of the convection looks to be going straight east, the lower clouds headed more NE.
Member Since: August 10, 2005 Posts: 162 Comments: 37829
167. weatherboykris
4:40 AM GMT on December 14, 2006
I think, accounting for the fact the latest forecast is already too far north,this will be mainly a south Florida event.Don't expect much in Central Florida.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
166. weatherboykris
4:36 AM GMT on December 14, 2006
If you compare the 00z GFS 6 hour forecast to current radar,it will verify too far north.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
165. HadesGodWyvern (Mod)
3:51 AM GMT on December 14, 2006
Five names were retired in the 2006 Pacific Typhoon Season

Chanchu, Bilis, Xangsane, Saomai, and Durian

Also the following names were replaced from the names retired in 2005

Longwang "Dragon King" was replaced by Haikui "sea anemone"

couldn't find info on the other two that were retired last year, must still be thinking of names.
Member Since: May 24, 2006 Posts: 50 Comments: 45295
164. hurricane23
3:43 AM GMT on December 14, 2006
Here is a piece from earlier from the miami NWS.

000
FXUS62 KMFL 140115
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
815 PM EST WED DEC 13 2006

LOW LEVEL EASTERLY WINDS...THOUGH WEAKENING...STILL ADVECTING
ISOLATED TO WIDELY SCATTERED LIGHT RAIN SHOWERS UPON THE E COAST.
BUT THIS IS NOT THE ONLY SHOWER ACTIVITY AFFECTING S FLA AS LIGHT
SHOWERS MOVING NE ACROSS THE SE GULF OF MEXICO FROM A DEVELOPING LOW
PRES SYSTEM JUST NW OF THE W TIP OF CUBA. IR SATL LOOPS INDICATE
COOLING TOPS MEANING STRENGTHENING CONVECTION. AS THE EVENING
PROGRESSES...CURRENT ISOLATED LIGHT SHOWERS WILL INCREASE AND BECOME
SCATTERED...AFFECTING MAINLY THE W COAST FROM NAPLES N AND INLAND
TOWARD LAKE OKEE AND PALM BEACH. CURRENT ZFP PACKAGE HAS THIS TREND
AND NO CHANGES ARE ANTICIPATED.
Member Since: May 14, 2006 Posts: 8 Comments: 13786
163. 882MB
1:43 AM GMT on December 14, 2006
Just looking at the GULF OF MEXICO satellite loop shows a cluster of thunderstorms where the low pressure will develop cooling which means there strengthening!
Member Since: September 29, 2006 Posts: 0 Comments: 360
161. hurricane23
1:06 AM GMT on December 14, 2006
882MB lets if this potential heavy rain event for south florida actually materializes.Over all models are in pretty good agreement of a pretty wet scenerio coming into play.

Here is the CMC rainfall forcast showing some descent rainfall across the area.
Member Since: May 14, 2006 Posts: 8 Comments: 13786
160. lightning10
12:50 AM GMT on December 14, 2006
Southern Californa doesnt need more rain it needs more wind cause thats what it looks like. This is a photocopy of every other storm that looked good so far this fall and it turns out like this...

main concern is the drastic change of the 12z and 18z GFS and
European model runs for this weekend's storm. The latest model runs
indicate that the trough will not be as deep as once advertised. The
closed low is now well to the east over Arizona by Monday. Although this has
been just a couple of runs...confidence is greater that this will
become more of a wind event then rain event


This fall has been just like a La Nina more then an El Nino down here and this is just more evidence.
Member Since: November 24, 2005 Posts: 41 Comments: 630
159. weatherboykris
12:24 AM GMT on December 14, 2006
TC report on Chris is out.
Member Since: December 9, 2006 Posts: 125 Comments: 11346
158. 882MB
11:54 PM GMT on December 13, 2006
Yes we need the rain! Seems like the latest MODELS indicate that the heavy rainfall we can get here in S.FLORIDA can last more into the weekend: PARTLY CLOUDY CONDITIONS PERSIST ACROSS SOUTH FLORIDA THIS
AFTERNOON...WITH A GOOD COVERAGE OF CUMULUS AND INCREASING AMOUNTS
OF HIGH-LEVEL CLOUD COVER COURTESY OF DEVELOPING CYCLONE BETWEEN
THE WESTERN TIP OF CUBA AND THE YUCATAN PENINSULA. SHORT TERM
MODELS ARE IN GENERAL AGREEMENT ON A SLOW DEEPENING OF THE LOW-
LEVEL CYCLONE...AS WEAK HEIGHT FALLS GRADUALLY SPREAD EASTWARD
ACROSS THE GULF IN ADVANCE OF MID-LEVEL SHORTWAVE TROUGH AND
ASSOCIATED UPPER-LEVEL SPEED MAX CURRENTLY MIGRATING ACROSS
NORTHERN MEXICO. AS THIS OCCURS...LOW-LEVEL FLOW WILL VEER TO THE
SOUTH...WITH RICH TROPICAL MOISTURE ADVECTED NORTHWARD ACROSS THE
FLORIDA PENINSULA. THE COMBINATION OF DEEP WARM ADVECTION AND
MODERATELY STRONG SYNOPTIC SCALE FORCING WILL RESULT IN
DEVELOPMENT OF A WIDESPREAD AREA OF RAINFALL/THUNDERSTORMS BY
THURSDAY AFTERNOON...
WITH THIS ACTIVITY LIKELY BEING MOST
CONCENTRATED ALONG SURFACE BAROCLINIC ZONE LOCATED SOMEWHERE
ACROSS THE CENTRAL PORTION OF THE FLORIDA PENINSULA. THUS...WILL
PLACE LIKELY POPS ACROSS THE NORTHWESTERN COUNTIES OF THE FORECAST
AREA...AND GRADUALLY TAPER THEM OFF TO THE SOUTHEAST...AS WEAK
UPPER RIDGING WILL BE MORE ESTABLISHED IN THIS AREA.

CURRENT INDICATIONS ARE THAT RAIN AND EMBEDDED THUNDERSTORMS WILL
CONTINUE FOR MUCH OF THE DAY ON FRIDAY AND FOR THE FIRST HALF OF
SATURDAY...BEFORE THE ENTIRE SYSTEM SLOWLY DRIFTS EASTWARD INTO
THE ATLANTIC. DESPITE FAIRLY CONSISTENT SOLUTIONS OFFERED BY THE
NAM/GFS...AS WELL AS THE UKMET/CMC...IT MUST BE EMPHASIZED THAT
THE PREVIOUSLY MENTIONED UPPER LOW OVER NORTHERN MEXICO MAY TEND
TO CUT OFF AND MOVE SLOWER THAN CURRENT GUIDANCE IS INDICATING...
WHICH WOULD RESULT IN RAIN CHANCES LINGERING THROUGH MORE OF THE
WEEKEND.
THIS TREND IS EXHIBITED MOST BY THE LATEST RUN OF THE
ECMWF.
OVERALL THE MAIN THREATS FROM THIS ACTIVITY WILL BE
LOCALLY HEAVY RAINFALL...AS PWAT VALUES ARE PROGGED TO APPROACH
OR SLIGHTLY EXCEED 2 INCHES...AND CLOUD TO GROUND LIGHTNING
STRIKES WITH ANY EMBEDDED CONVECTIVE CELLS.
Member Since: September 29, 2006 Posts: 0 Comments: 360
156. 882MB
11:30 PM GMT on December 13, 2006
I knew something was gonna happen with 96W since I saw it developing on monday night! It covers a very large area, this tends to slow the strengthening process, like HURRICANE HELENE last year which was large in size when it came off of AFRICA it developed slowly due to its huge size.
Member Since: September 29, 2006 Posts: 0 Comments: 360
155. wayneah
10:58 PM GMT on December 13, 2006
Dr. Jeff,

Any chance that global warming could introduce a variable into hurricane development that nobody has considered - specifically an increase in African dust? It would seem that if global warming increased drought in Africa, as many models suggest, then this inhibitor could be come more frequent, making hurricanes less frequent. Might help a bit if warmer SSTs lead to more intense hurricances.
152. 1900hurricane
9:50 PM GMT on December 13, 2006
Gotta run! Just wait until Wednsday. Because my last day of school is Tuesday, I will be able to blog for as long as I want until school resumes in January! Have a great day!

: )
Member Since: August 2, 2006 Posts: 46 Comments: 11667
151. ryang
9:49 PM GMT on December 13, 2006
So that invest does look impreesive.
Member Since: August 25, 2006 Posts: 329 Comments: 12432
150. 1900hurricane
9:46 PM GMT on December 13, 2006
Hello ryang.
Member Since: August 2, 2006 Posts: 46 Comments: 11667
149. ryang
9:43 PM GMT on December 13, 2006
Hi 1900.
Member Since: August 25, 2006 Posts: 329 Comments: 12432
148. 1900hurricane
9:38 PM GMT on December 13, 2006
Hello Y'all! W.Pac. Invest certanly looks impressive.

Link
Member Since: August 2, 2006 Posts: 46 Comments: 11667
147. turtlehurricane
9:16 PM GMT on December 13, 2006
A significant rainfall event is still on tap for central and south florida, read more on my blog or

Florida weather
Member Since: July 22, 2005 Posts: 227 Comments: 469
146. Drakoen
8:59 PM GMT on December 13, 2006
interesting area of moderate to heavy convection in the southwestern carribean. Probably will go inland though.
Member Since: October 28, 2006 Posts: 57 Comments: 30489
145. Drakoen
8:55 PM GMT on December 13, 2006
probabaly won't. Look at the model tracks. They take it right into the phillipines once again. probably get super typhoon status like the rest of them did.
Member Since: October 28, 2006 Posts: 57 Comments: 30489

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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.