NOAA predicts a near-normal Atlantic hurricane season
NOAA forecasts a near-normal Atlantic hurricane season in 2012, in their May 24 outlook. They give a 50% chance of a near-normal season, a 25% chance of an above-normal season, and a 25% chance of a below-normal season. They predict a 70% chance that there will be 9 - 15 named storms, 4 - 8 hurricanes, and 1 - 3 major hurricanes, with an Accumulated Cyclone Energy (ACE) 65% - 140% of the median. If we take the midpoint of these numbers, NOAA is calling for 12 named storms, 6 hurricanes, 2 major hurricanes, and an ACE index 102% of normal. This is very close to the 1981 - 2010 average of 12 named storms, 6 hurricanes, and 3 major hurricanes. Hurricane seasons during the active hurricane period 1995 - 2011 have averaged 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 153% of the median. Only five seasons since 1995 have not been above normal--including four El Niño years (1997, 2002, 2006, and 2009), and the neutral 2007 season.
Figure 1. The strongest Atlantic hurricane of 2011, Ophelia, as seen at 1:40 pm EDT October 1, 2011. At the time, Ophelia was a Category 3 hurricane with 120 mph winds. At 11 pm that night, Ophelia peaked at Category 4 strength with 140 mph winds. Image credit: NASA.
The forecasters cited the following main factors that will influence the coming season:
1) Near-average sea surface temperatures (SSTs) are expected in the hurricane Main Development Region (MDR), from the Caribbean to the coast of Africa between between 10°N and 20°N. SSTs in the MDR during April were near-average, and are expected to remain so during hurricane season, based on current observations, climatology, and long-range model forecasts.
2) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO): "During 1995-2010, some key aspects of the tropical multi-decadal signal within the MDR have included reduced vertical wind shear and weaker easterly trade winds, below-average sea-level pressure, a configuration of the African easterly jet that is more conducive to hurricane development from tropical cloud systems (aka Easterly waves) moving off the African coast, and warmer than average SSTs."
3) An El Niño event may occur this year: "Another climate factor known to significantly impact Atlantic hurricane activity is the El Niño-Southern Oscillation (ENSO.) The three phases of ENSO are El Niño, La Niña, and ENSO-Neutral. El Niño events tend to suppress Atlantic hurricane activity, while La Niña events tend to enhance it (Gray 1984). If El Niño fails to develop, the probability of an above-normal Atlantic hurricane season will be higher and the actual seasonal activity will likely be toward the upper end of our predicted ranges." There is currently of lot of uncertainty whether or not an El Niño event will develop in time for the August - September - October peak of hurricane season--the latest NOAA El Niño discussion is giving a 41% chance of an El Niño event during hurricane season, and a 48% chance of neutral conditions.
4) NOAA is increasingly using output from ultra-long range runs of the computer forecast models we rely on to make day-to-day weather forecasts, for their seasonal hurricane forecasts: "The outlook also takes into account dynamical model predictions from the NOAA Climate Forecast System (CFS), the European Centre for Medium Range Weather Forecasting (ECMWF), the United Kingdom Meteorology (UKMET) office, and the EUROpean Seasonal to Inter-annual Prediction (EUROSIP) ensemble. These models show large spreads in the ENSO forecasts for ASO, ranging from ENSO-Neutral to a moderate-strength El Niño episode. As a result, their forecasts for the Atlantic hurricane season also show a considerable spread, ranging from slightly above normal to slightly below normal."
How accurate are the NOAA seasonal hurricane forecasts?
A talk presented by NHC's Eric Blake at the 2010 29th Annual AMS Conference on Hurricanes and Tropical Meteorology studied the accuracy of NOAA's late May seasonal Atlantic hurricane forecasts, using the mid-point of the range given for the number of named storms, hurricanes, intense hurricanes, and ACE index. Over the past twelve years, a forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Using another way to measure skill, the Mean Squared Error, May NOAA forecasts for named storms, hurricanes, and intense hurricanes had a skill of between 5% and 21% over a climatology forecast. Not surprisingly, NOAA's August forecasts were much better than the May forecasts, and did significantly better than a climatology forecast.
Figure 2. Mean absolute error for the May and August NOAA seasonal hurricane forecasts (1999 - 2009 for May, 1998 - 2009 for August), and for forecasts made using climatology from the past five years. A forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.
I'll have an update on Hurricane Bud and Invest 94L Friday morning.
Jeff Masters
Reader Comments
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 — Blog Index
Unfortunately the heat remains stuck in the Southwest where the fire danger remains way up... Even worse it's forecast to stay dry out there.
I'm not sure how many or if they achieved hurricane strength. Here's TS Allison part one. :)
June 26-28th, 1989 (Allison): Allison formed from the remains of Pacific hurricane Cosme, which made landfall near Acapulco and accelerated northeast into the western Gulf. A new surface circulation formed in the western Gulf of Mexico and moved north-northeast, strengthening into a tropical depression and then a tropical storm offshore the Texas coastline. Winds gusted to 56 mph at Galveston on the 26th as Allison made landfall. One tornado touched down on the Bolivar peninsula and did minor damage (Lichter). Over 30 inches of rain led to severe flooding in extreme Southeast Texas...only ten years after the extreme flooding from Claudette. Eleven died during the storm. Damage from Allison totaled $500 million, putting it on the list of the United States%u2019 most damaging storms.
It appears most models like a Georgia landfall, as of late.
See post 16 or so in the blog... I totally agree... I really don't see much value in the NOAA numbers.
Would "Grothar" be considered a typo?
OH! Never mind. That would be a typo in my post and not yours. ;-)
Hmmm... Wasn't it an analogue for last season? Thought it was a double-dip.
12-15 Named Storms
6-8 Hurricanes
3-5 Major Hurricanes
Maybe the first 8 storms wont be TS like last year. That would lower the amount of Hurricanes and Major Hurricanes.
Pretty sure that blue bit covers 2008.
I think 2008 was a cool neutral year coming off a La Nina.
2008 was a neutral year
2010 = 2007 which were strong La Nina years that came off of Strong El Nino's the previous years (2006. and 2009).
2011 = 2008 Which were Weaker La Nina years that were fading into Neutral(2008 = neutral basically).
2011 and 2008 were considered 2nd year La Nina's because they were La Nina's during the beginning of the year.
.
I would have preferred if the Dr. gave his current thoughts on the tropics, but perhaps he doesn't think there's much difference between talking about it now or tomorrow.
Appears so as of now.
110 Mph- Peak.
Thanks, didn't realize that the recon mission hadn't taken place before the 6pmGMT(11amPDT) ATCF figures were posted.
Still surprised that the ATCF's MaxSusWinds number hasn't already been re-evaluated&altered to reflect the recon. Woulda thought a Major-to-Minor status-change would have been enough for them to take an edit-break into their regular posting schedule.
Ok, but it was coming off a pretty strong La Nina.
Just to clarify that graph a little, the blue does cover 2008 however most of that year was in a cool neutral phase not a La Nina... I think that little cut in the middle of that long blue period represents the 2008 season- still below normal, but above the -0.5 C needed for a La Nina
Broad/weak circulation. It's forecasted by many models now to become Beryl, and then get shoved down by the High, into SE coast.
Tomorrow it should really start developing. Though not sure if shear will die down at all.
35kts at surface
That's the thing. the 2007/2008 La Nina set up into 2009 is completely different, you see.
Weren't set to go into a full blown La Nina, and it will be much more of a gradual ease into El Nino.
Look at the early 2000's where the was no LARGE swings in La Nina-El Nino and vise-versa.
It peaks at 1004 mb the second time it goes north.
That would be interesting to have the same storm hit you twice.
Record heat triggers scatteredthunderstorms have across the Bay area near the end of the day Thursday.
The storms have lined up with the seabreeze, predominately along the coastal counties of Pinellas, Hernando, Pasco and Citrus Counties.
Expect heavy rain and lightning in these storms. Some storms could produce small hail.
Dime-size hail was reported in Odessa and Trinity around 6 p.m.
Tampa and Bradenton set records for high temperatures. Tampa set a new record at 96 degrees and Bradenton saw a record of 95 degrees.
Forecasted to by saturday, stated by NHC.
Its currently at 35 kts as of now.
2002 I would think, someone correct me if I'm wrong.
shear? or the storm?
Pretty active for this time of year in Africa, but they are a bit south right now.
Yes, but it has a more tropical structure in the image i posted.
the nam has the storm hugging the gulf coastline all the way to NOLA as a possible TD
"We have no idea what's going to happen anymore, so let's just see how things go."
It's certainly started out in an unpredictable manner, so it might very well stay that way.
Better than 2010's prediction of 14-23 storms. Wow, that really helped.
Viewing: 51 - 101
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 — Blog Index