Record Atlantic SSTs continue; very active hurricane season foreseen by CSU and TSR
Sea Surface Temperatures (SSTs) in the Atlantic's Main Development Region for hurricanes had their warmest March on record, according to an analysis of historical SST data from the UK Hadley Center. SST data goes back to 1850, though there is much missing data before 1910 and during WWI and WWII. The region between 10°N and 20°N, between the coast of Africa and Central America (20°W - 80°W), is called the Main Development Region (MDR) because virtually all African waves originate in this region. These African 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.) SSTs in the Main Development Region (10°N to 20°N and 20°W to 85°W) were an eye-opening 1.26°C above average during March. This easily beats the previous record of 1.06°C set in 1969. SSTs in the Main Development Region are already warmer than they were during late June of last year, which is pretty remarkable, considering that March is one of the coldest months of the year for SSTs in the North Atlantic. Last month's anomaly of 1.26°C tied with June 2005 as the greatest monthly anomaly ever recorded in the Atlantic MDR.
Figure 1. The departure of sea surface temperature (SST) from average for April 12, 2010. Image credit: NOAA/NESDIS.
What is responsible for the high SSTs?
As I explained in detail in last month's post on record February SSTs in the Atlantic, the Arctic Oscillation (AO) and its close cousin, the North Atlantic Oscillation (NAO), are largely to blame for the record SSTs. The AO and NAO are climate patterns in the North Atlantic Ocean related to fluctuations in the difference of sea-level pressure between the Icelandic Low and the Azores-Bermuda High. If the difference in sea-level pressure between Iceland and the Azores is small (negative NAO), this creates a weak Azores-Bermuda High, which reduces the trade winds circulating around the High. During December - February, we had the most negative AO/NAO since records began in 1950, and this caused trade winds between Africa and the Lesser Antilles Islands in the hurricane Main Development Region to slow to 1 - 2 m/s (2.2 - 4.5 mph) below average. Slower trade winds mean less mixing of the surface waters with cooler waters down deep, plus less evaporational cooling of the surface water. As a result, the ocean heated up significantly, relative to normal, over the winter. This heating is superimposed on the very warm global SSTs we've been seeing over the past few decades due to global warming. Global and Northern Hemisphere SSTs were the 2nd warmest on record this past December, January, and February. We are also in the warm phase of a decades-long natural oscillation in Atlantic ocean temperatures called the Atlantic Multi-decadal Oscillation (AMO). This warm phase began in 1995, and has been partially responsible for the high levels of hurricane activity we've seen since 1995.
What does this imply for the coming hurricane season?
The high March SST anomaly does not bode well for the coming hurricane season. The three past seasons with record warm March SST anomalies all had abnormally high numbers of intense hurricanes. Past hurricane seasons that had high March SST anomalies include 1969 (1.06°C anomaly), 2005 (0.93°C anomaly), and 1958 (0.93°C anomaly). These three years had 5, 7, and 5 intense hurricanes, respectively. Just two intense hurricanes occur in an average year. The total averaged activity for the three seasons was 15 named storms, 11 hurricanes, and 6 intense hurricanes (an average hurricane season has 10, 6, and 2.) Both 1958 and 2005 saw neutral El Niño conditions, while 1969 had a weak El Niño. So, even if this year's El Niño lingers on into hurricane season, it may not protect us from a hyper-active hurricane season--the weak El Niño year of 1969 had 18 named storms, 12 hurricanes, and 5 intense hurricanes.
April forecast for the 2010 Atlantic hurricane season issued by Colorado State University
A well above-average Atlantic hurricane season is on tap for 2010, according to the latest seasonal forecast issued last week by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The Klotzbach/Gray team is calling for 15 named storms, 8 hurricanes, and 4 intense hurricanes. An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The forecast calls for 30% above-average chance of a major hurricane hitting the U.S., both along the East Coast (45% chance, 31% chance is average) and the Gulf Coast (44% chance, 30% chance is average). The Caribbean is also forecast to have an above-average risk of a major hurricane (58%, 42% chance is average.)
The forecasters cited two main reasons for their forecast of an active season:
1) Sea surface temperature (SST) anomalies in the tropical Atlantic are at their warmest levels on record in the Main Development Region for hurricanes in the tropical Atlantic. Warmer-than-normal waters provide more heat energy for developing hurricanes. In addition, an anomalously warm tropical Atlantic is typically associated with lower sea level pressure values and weaker-than-normal trade winds, indicating a more unstable atmosphere with decreased levels of vertical wind shear, favoring hurricane development. Part of the reason for the substantial warming is because a weaker than average Bermuda-Azores High drove weak trade winds over the winter and early spring. These weaker winds acted to reduce evaporative cooling of the ocean. Weaker winds also decreased the mixing of cool waters to the surface from below.
2) Hurricane activity in the Atlantic is lowest during El Niño years and highest during La Niña or neutral years. The CSU team expects the current weak to moderate El Niño conditions to transition to neutral and perhaps weak La Niña conditions by this year's hurricane season. April and May are typically the months when the atmosphere will swing between El Niño and La Niña, which makes any seasonal forecasts of hurricane activity during April low-skill. The current computer models used to predict El Niño (Figure 2) mostly favor neutral conditions for the coming hurricane season. The models used include statistical models, which observe how previous El Niño events have evolved, and sophisticated computer-intensive dynamical models (similar to the GFS model we use to make weather forecasts). The reliability of all of these models is poor, but the CSU team believes the ECMWF model (yellow-orange squares) is the best one. The ECMWF model only goes out to JJA (June-July-August) in this plot, and is forecasting neutral conditions.
Figure 2. Computer model forecasts of El Niño/La Niña made in March. The forecasts that go above the red line at +0.5°C denote El Niño conditions; -0.5°C to +0.5°C denote neutral conditions, and below -0.5°C denote La Niña conditions. Three computer models predict El Niño conditions and three predict La Niña for the upcoming hurricane season (ASO, August-September-October). However, most of the models predict neutral conditions. Image credit: Columbia University's IRI.
Analogue years
The CSU team picked five previous years when atmospheric and oceanic conditions were similar in April to what we are seeing this year. Those five years were 2005, the most active Atlantic season in history; 1998, which had Category 5 Hurricane Mitch in the Western Caribbean; 1969, which featured Category 5 Hurricane Camille, the strongest hurricane ever to hit the U.S.; 1966, which had Category 4 Hurricane Inez that killed 1,000 people in the Caribbean and Mexico; and 1958, which had five major hurricanes. The mean activity for these five years was 16 named storms, 10 hurricanes, and 5 intense hurricanes.
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 no skill in predicting the future. This year's April forecast uses the same formula as was used in 2008 and 2009. This scheme successfully predicted an active hurricane season in 2008, 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 on June 2, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years.
2010 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR), issued their 2010 Atlantic hurricane season forecast last week, and they are also calling for a very active year: 16.3 named storms, 8.5 hurricanes, and 4.0 intense hurricanes. TSR predicts a 74% chance of an above-average hurricane season, 20% chance of a near-normal season, and only a 6% chance of a below normal season. They give a 77% chance that 2010 will rank in the top third of most active hurricane seasons on record.
Like the CSU April forecasts, the TSR April forecasts have little skill. I like how TSR puts their skill level right next to the forecast numbers: 12% skill above chance at forecasting the number of named storms, 7% skill for hurricanes, and 6% skill for intense hurricanes. That's not much better than flipping a coin.
TSR projects that 5.1 named storms will hit the U.S., with 2.3 of these being hurricanes. The averages from the 1950 - 2009 climatology are 3.2 named storms and 1.5 hurricanes. Their skill in making these April forecasts for U.S. landfalls is 9 - 13% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.6 named storms, 0.7 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.
TSR cites two main factors for their forecast of an active season: they predict slower than normal trade winds from July - September over the Main Development Region (MDR) for hurricanes over the Atlantic (the region between 10° - 20° N from Central America to Africa, including all of the Caribbean). Trade winds are forecast to be 0.81 meters per second (about 2 mph) slower than average in this region, which would create greater spin for developing storms, and allow the oceans to heat up due to reduced evaporational cooling and reduced mixing of cooler sub-surface waters to the surface. TSR forecasts that SSTs will be 0.42°C above average in the MDR during hurricane season.
Figure 3. Accuracy of long-range forecasts of Atlantic hurricane season activity performed by Phil Klotzbach and Bill Gray of Colorado State University (colored squares) and TSR (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.
I'll have a new post by Thursday.
Jeff Masters
Reader Comments
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No correlation
Thanks, nrt. Good reminder (I had been exposed to this once upon a time...)
Parlaying this: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.28.9627&rep=rep1&type=pdf
into current SST obs in both regions defining the dipole, one would think that the Sahel rainfall for the duration of summer would be...
...
about normal.
Looking for more.
Hey I heard it too!! Just wait till Hurricane season starts!!
We're is an "unusual early summer-like" pattern, per the NWS Area Forecast Discussion earlier today. It's beautiful, but this is our normal rainy season, and no real good rain chances are forecasted for this week!
Awesome, considering we had a very wet winter. Hopefully we get a good rain soon, it's going on 3 weeks!
I was thinking ACE seemed a limit a month or more ago but just checked that. Last year S Hem only ended up with 57% of it's normal ACE.. it seemed to slowly increase through the season with N Hem having 82% normal. N Atl only had 50% & of course the EPAC was the winner with El Nino coming on with 96% of normal. S Hem seemed to have a slower start but is up to 193 with 204 being normal. It still may make 100% as season there isn't over. Shows overall ACE near normal & trending up..I'd expect normal or above.
Hello, hello, hello...Echo, echo, echo.
The weather is fairly quiet in the US, there was heavy rain in CA, that caused a terrible traffic accident early this morning that killed 5 people, a couple of hail reports, a small tornado near Belle Glade in FL, that's about it!!
The Tutt Low's that develop in the Atlantic Ocean may possibly put a damper on TC development. However, 2010 will most likely be alot busier than 2009.
2010 TC Activity
Updated April 12, 2010 12Z
BASIN 2010 ACE NORMAL YEARLY ACE**
Southern Hemisphere 193 204
Northern Hemisphere 2.0075 563
New sun spot
I think that, because, with in 2005, maybe this trend will continue, Hurricanes Katrina, Rita, and Wilma all weakened to significantly weaker storms before they hit the coast. Rita had winds of 180 mph, and hit the coast as a Minimal Cat 3!
Stormchaser2007, I see your point with the models, but I have a funny feeling that some will weaken when they go to the coast, because the history, favors it. Take Hurricane Dennis for example. It was a powerful 150 mph hurricane, but the eyewall collapsed, right when it hit the coast. There appeared to be dry air weaving into Dennis. But we shall see who's right though, as the hurricane season goes on, and as La Nina prevails...
http://spaceweather.com/
Amazing 6.3 Mw earthquake in southern Spain yesterday, with no damage or injuries reported, due to its deep location.
A handful of 4.5-5.1 Mw quakes in the Philippines, near New Guinea and is southern Mexico earlier today.
This is unusual, hopefully things don't ramp up
Yes, things are eerily quiet today, weather-wise and earthquake-wise.
SPC Preliminary Storm Reports for-12-10 :
Wow, atmo, I knew it was slow...
Pretty cold winter. Pretty anemic moisture return along with that.
Well, you beat me to it :o)!!
Concerning the uptick in 2005 rainfall:
"In the western part of the Sahel, the rainfall season was marked by highly frequent heavy rainfall episodes. The rainfall increase was even more significant (Fig. 1) and resulted in flooding in many locations and an increase in infectious disease outbreaks, mainly cholera and malaria. This marks a sharp contrast from the long term drying trend that started in the early 70s and continued into the 80s and the 90s. Over the past 3 years, the coupled ocean – atmosphere system has been quite similar to observed conditions during the 50s and 60s. In particular, during the 2005 rainfall season, the Atlantic dipole mode (ADM) featuring a warm tropical north Atlantic and a cool Gulf of Guinea was quite prominent. This is a known mode of variability of Sahel rainfall on the interdecadal time scale and is conducive to enhanced rainfall across the Sahel (Lamb et al., 1992). The ADM appeared during the spring and persisted throughout the summer."
http://docs.google.com/viewer?a=v&q=cache:C0P7R1PFx10J:www.clivar.org/organization/vacs/docs/Sahel3 .pdf+tropical+atlantic+dipole+sahel&hl=en&gl=us&pid=bl&srcid=ADGEESjZk8q0kryh6yEQNohVBTDXOdfLyvUGEZA Xpzu2K0gsPK9kuOv0CtIyUF2qqf8HI-K8OBsFxGOtDLyVvkrxROvLacCH5kl9_XOyCT_vWnBpG1RqNin1KoGiK5Y2rlMK41eefar O&sig=AHIEtbTpQAKhKAPoKxT4jpUuTqw6SqSZtA
So this leads to the question: Does our current SST anomaly in the Gulf of Guinea qualify as "cool" to satisfy the conditions "the Atlantic dipole mode (ADM) featuring a warm tropical north Atlantic and a cool Gulf of Guinea was quite prominent"?
It is a bit cooler WRT to the MDR and immediate African Atlantic coast north of the equator, but I don't think it is "cool".
Currently stuck at no reason to foresee any more than a normalish rainfall amount for the Sahel.
)
104 Tornado reports Jan through March 05
236 Jan through April of 2005.
April was very busy (132 reports).
But the wildflowers are outstanding this year. I was just up there, and the drive up I-45 and back was marvellously colorful.
Actually, it is because of the very cold, wet winter we had this year that they are so beautiful. Now, if only all the uncut brown tropicals that folks are ignoring (down here in Houston) would go away this would make things nicer.
3 inches short of rainfall and a PWS recording close to 90 a week ago Saturday.... ACs running... does not bode well.
Tornado season this year appears to be coming in outbursts. Especially that spike in January which was likely caused by the clashing of warm and AO-negative cold air.
Last 6 years plotted together. El Nino is bad for TCs before it's peak and bad for tornadoes the following spring.
2005 in green, 2010 in red:
A portion of the NWS DFW, TX Area Forecast Discussion from 3:42PM CDT today:
LONG TERM...
THE SUMMERLIKE PATTERN WILL CONTINUE TO INFLUENCE
OUR WEATHER THROUGH THE WEEKEND. THE STRONG RIDGE CENTERED IN THE
SOUTHEASTERN CONUS WILL KEEP MOST OF NORTH TEXAS DRY. HOWEVER...A
SERIES OF SHORTWAVES COULD BRING SOME THUNDERSTORMS TO AREAS WEST
OF INTERSTATE 35. THE FIRST SHORTWAVE WILL ENTER THE WESTERN ZONES
THURSDAY AFTERNOON BRINGING A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS. IT LOOKS UNLIKELY ANY AREAS EAST OF INTERSTATE 35
WILL SEE ANYTHING DUE TO A STRONG CAP RESULTING FROM RIDGE
SUBSIDENCE AND THE NORTHEASTERLY MOTION OF THE SHORTWAVE. THE NEXT
SHORTWAVE IS CONSIDERABLY STRONGER...PER THE GFS...AND
SUCCESSFULLY BREAKS DOWN THE SOUTHEASTERN CONUS RIDGE AS IT MOVES
NORTHEAST ACROSS NORTH TEXAS ON SATURDAY. PRECIP WITH THIS
SHORTWAVE WILL LIKELY REMAIN CONCENTRATED WEST OF I-35 AS WELL
BECAUSE THE MID-LEVELS WILL STILL BE TOO DRY TO THE EAST. A VERY
WEAK COLD FRONT TRIES TO MOVE THROUGH OKLAHOMA SATURDAY. THE GFS
STALLS IT ALONG THE RED RIVER SATURDAY AFTERNOON WHILE THE ECMWF
MOVES IT THROUGH EARLY SATURDAY MORNING. THE ECMWF SOLUTION LOOKS
UNLIKELY AT THIS TIME AS IT LACKS THE UPPER LEVEL SUPPORT TO PUSH
THROUGH NORTH TEXAS LATE FRIDAY NIGHT/EARLY SATURDAY MORNING. THE
GFS SOLUTION APPEARS MORE LIKELY AND AS SUCH WENT WITH THE GFS FOR
THE MAJORITY OF THE LONG TERM FORECAST. IN SUMMARY...SUMMERLIKE
PATTERN WILL BRING THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS...
MAINLY WEST OF INTERSTATE 35...THROUGH THE REMAINDER OF THE
FORECAST PERIOD. 42/MM
Yeah, the good ol' Louisiana coffee must have you bouncing off the walls. As for me, I gave my body a break from coffee today!
??? Is beell over here?
(no way is he drinking the chickory)
I don't think it will be really high above normal, but even having it at normal coupled with the last 3 wet years probably wouldn't limit TCs in the Atlantic.
Chickory is for Civil War Veterans...
http://howto.wired.com/wiki/Chase_Storms
Spring has been late. I think the tornado season skipped the Gulf Coast mostly. (Tell that to the people who had severe thunderstorms, of course.)
All I've heard for the last month and a half is how warm the MDR is and how we'll have more tropical cyclones than cockroaches.
So would you agree that it is not quite shaping up to a +700 mm anomaly as seen in 2005? (in the Senegal region, as per the link I posted)
Notable (but with the usual data reliability caveats) is the 1958 Sahel anomaly. Much higher than 2005.
No, you are correct. Our usual peak season for severe weather is Feb (and Nov). Feb went out like a lamb...March, too.
Thanks for the reply, that was my impression as well. Honestly, I can't wait for some nice warm weather. I'm going skiing with the daughter and a granddaughter tomorrow but I am getting tired of the cold. It would be fun to feel some warm tropical water again. I'm looking forward to that someday soon.
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