NOAA's forecast: a very active, possibly hyperactive Atlantic hurricane season
The National Oceanic and Atmospheric Administration (NOAA) issued its 2010 Atlantic hurricane season forecast today. NOAA forecasts a very active and possibly hyperactive season. They give an 85% chance of an above-normal season, a 10% chance of a near-normal season, and just a 5% chance of a below-normal season. NOAA predicts a 70% chance that there will be 14 - 23 named storms, 8 - 14 hurricanes, and 3 - 7 major hurricanes, with an Accumulated Cyclone Energy (ACE) in the 155% - 270% of normal range. If we take the midpoint of these numbers, NOAA is calling for 18.5 named storms, 11 hurricanes, 5 major hurricanes, and an ACE index 210% of normal. A season with an ACE index over 175% is considered "hyperactive." An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The forecasters note that in regards to the oil spill in the Gulf of Mexico,
"Historically, all above normal seasons have produced at least one named storm in the Gulf of Mexico, and 95% of those seasons have at least two named storms in the Gulf. Most of this activity (80%) occurs during August-October. However, 50% of above normal seasons have had at least one named storm in the region during June-July."
The forecasters cited the following main factors that will influence the coming season:
1) Expected above-average SSTs in the hurricane Main Development Region (MDR), from the Caribbean to the coast of Africa. SSTs in the MDR are currently at record levels, and the forecasters note that several climate models are predicting record or near-record SSTs during the peak portion of hurricane season (August - October.) "Two other instances of very warm SSTs have been observed in the MDR during February-April (1958 and 1969). In both years, the SST anomaly subsequently decreased by roughly 50% during the summer months. For 2010, although the record SST departures may well decrease somewhat, we still expect a continuation of above average SSTs throughout the Atlantic hurricane season. "
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 1995-2009, some key aspects of the tropical multi-decadal signal within the MDR have included warmer than average SSTs, reduced vertical wind shear and weaker easterly trade winds, below-average sea-level pressure, and a configuration of the African easterly jet that is more conducive to hurricane development from tropical waves moving off the African coast. Many of these atmospheric features typically become evident during late April and May, as the atmosphere across the tropical Atlantic and Africa begins to transition into its summertime monsoon state."
3) There will either be La Niña or neutral conditions in the Equatorial Eastern Pacific. El Niño is gone, and it's demise will likely act to decrease wind shear over the tropical Atlantic, allowing more hurricanes to form. "La Niña contributes to reduced vertical wind shear over the western tropical Atlantic which, when combined with conditions associated with the ongoing high activity era and warm Atlantic SSTs, increases the probability of an exceptionally active Atlantic hurricane season (Bell and Chelliah 2006). NOAA's high-resolution CFS model indicates the development of La Niña-like circulation and precipitation anomalies during July."
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 (Figure 2). Not surprisingly, NOAA's August forecasts were much better than the May forecasts, and did significantly better than a climatology forecast.
Figure 1. 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.
How do NOAA's seasonal hurricane forecasts compare to CSU and TSR?
Two other major seasonal hurricane forecasts will be released next week. On June 2, Phil Klotzbach and Bill Gray of Colorado State University (CSU) issue their forecast, and the British firm Tropical Storm Risk (TSR) will issue their outlook on June 4. A three-way comparison of the forecast accuracy of the three groups' forecast (Figure 2) reveals that all three organizations enjoy some success at making accurate seasonal forecasts, with NOAA and CSU making the best late May/early June forecasts overall. While the skill of these forecasts is low, they are useful for businesses such as the insurance industry.
Figure 2. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August). using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.
Central American disturbance
The Atlantic is currently quiet, with the non-tropical storm (90L) that we were watching now no longer a concern. There is an area of disturbed weather (90E) just off the Pacific coast of Mexico that will be a major concern for southern Mexico and much of Central America over the next 3 - 4 days. The disturbance will bring heavy rains to Central America during the remainder of the week, potentially bringing serious flooding rains to portions of Mexico, Guatemala, El Salvador, Honduras, and Nicaragua. NHC is giving the disturbance a high (>60% chance) of the disturbance developing into a tropical depression by Saturday. There is the potential for disturbed weather accompanying the disturbance--or the disturbance itself--to push into the Western Caribbean early next week and pose a threat to develop into a tropical depression. While there is high wind shear over the northern Caribbean, shear may be low enough to allow development should the disturbance stay in the southern reaches of the Caribbean. None of the models are currently calling for this to happen, and I think the threat is low. Any storm that develops in the Caribbean in the coming week would get steered to the northeast and will not pose a threat to the Gulf of Mexico. Wunderbloggers Weather456 and StormW have more on the tropics.
Figure 3. Visible satellite image of the Central American disturbance 90E this morning.
Oil threat for the coast of Louisiana to decrease this weekend
Light winds from the north or west are expected to prevail across the northern Gulf of Mexico through Friday, resulting in a lessened threat of oiling to the Louisiana shoreline, according to the latest trajectory forecasts from NOAA. However, the latest runs of the GFS model indicate a return to onshore winds out of the southwest for most of next week, which will likely bring oil back towards shore. At greatest risk will be the coast of Louisiana, and there will be heightened risk to Mississippi, Alabama, and the Florida Panhandle. I'll a have a more in-depth discussion of the oil spill forecast in Friday's blog.
Oil spill resources
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami
Join the Hurricane Haven with Dr. Jeff Masters: a new Internet radio show
Beginning next week, I'll be experimenting with a live 1-hour Internet radio show called "Hurricane Haven." The show will be aired at 4pm EDT on Tuesdays, with the first show June 1. Listeners will be able to call in and ask questions. Some topics I'll cover on the first show:
1) What's going on in the tropics right now
2) Preview of the coming hurricane season
3) How a hurricane might affect the oil spill
4) How the oil spill might affect a hurricane
5) New advancements in hurricane science presented at this month's AMS Conference on Hurricanes and Tropical Meteorology
6) Haiti's vulnerability to a hurricane this season
I hope you can tune in to the broadcast, which will be at http://www.wunderground.com/wxradio/wubroadcast.h tml. If not, the show will be recorded and stored as a podcast.
Jeff Masters
Reader Comments
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OoOo... When and where will Alex make landfall, is it Florida, the Gulf Coast??? :P
BOTH! The gulf coast of Florida, ghost storm alerts to follow...
Not discounting the possibilities raised in the article but sounds a little "hypish" to me and capitalizing on the current Gulf crisis......We've had a few strong storms come through the Gulf in recent years, this issue has not occured (to public knowledge anyway) and they normally shut down the rigs and evacuate when a storm threatens.
The problem is that the existing pipelines survived CAT5 Katrina, CAT5 Rita and a small host of smaller hurricanes in the last 6 years or so...this study sounds a little more alarmist than alarming
Well aren't you just a bundle of joy. ;)
Hi Barbara!
You got it wrong, it's obviously going to head off the east coast, swerve west randomly, and hit Delaware. :P
14-23 storms? That's the biggest range I've ever seen.
Category 5 ghost storm landfalls, people should prepare LOL..
LOL! You're way late with that observation! :D
Watch yourself, mister...you can find yourself in serious trouble in here posting stuff like that!
If someone downcasts this one I'm leaving and never coming back. In fact it has developed an eye feature and should be named already (looks fully tropical). The only real difference between this and 90L though is no shear.
98s:
90l:
Ok...like I haven't killed the dog that is 90L enough already! :P
BANG 90L...YOU'RE DEAD!
or Castrol motor oil. Not that it matters because any oil BP pumps out gets sold on the world market so even if you went to AMOCO or CHEVRON or SHELL you still might be pumping BP.
They could have at least aimed it north for the 3 or 5 days, as the models show. That was just laziness.
Very true LOL. Nothing like old news !
I just took a look at the shear map and noticed that the high pressure that was offshore near 90E has now moved off to the NE and is onshore in El Salvador just East of the border with Guatemala. If this continues to push off to the NE and gets into the NW Caribbean things could get interesting. Already it has resulted in shear falling off in the Gulf of Honduras.
I thought it was going to hit Connecticut while somehow avoiding Long Island... :P
Thanks for the shout a while back in the blog. Unless something changes I will mostly be lurking this season as link to web where I live has become very problematic.
Shen
I can see his update being down from the "South Florida shower curtain weather desk" lol
I've thought about getting something similar. I have noticed that the local BP station looks a little empty when I drive by it. I think I'm not the only one who won't be going back.
IRONY FTW!
I can't control that, but I sure can control not going to a BP.
Brother, we'll be looking for you...a word of warning though: if there is a major landfall in the CONUS I will pretty much disappear (work you know)
Good seeing you, man!
I was also thinking that in this scenario it is possible that this could hurt 90E and aid in whatever wants to develop in the Caribbean
Flood, weathermanwannbe, Dan (Hi!). I just wanted to share this; can't evaluate it. The existing spill is really "enough".
i am supporting you. its just that anything short of ditching your car means you will be driving on BP fuels
It's not dead till it's completely dissipated and unrecognizable. Refer back to Fred (2009)... near-naked swirl across the entire Atlantic but lead to severe flooding in Georgia.
Don't mind them. I look forward to your update. Please let me know if you think Tampa is in any danger this year. Thanks!
The great thing is I thought about using that as my example, along with an oddball New Hampshire hit. I've spent way too much time visiting relatives in the northeast...
And wow, that subtropical storm really does look tropical to me. The Navy claims it's under 30-50 knots of shear, but I'm not buying it...
The oil is 3000 feet below sea level. No collapse.
Weather blog here
OIL blog here
Join the club, never again.
Yes, it could indeed. A high that is offset from a surface low feature will impart shear to it. In fact, if you look at the shear tendency map for 90E you will see that only a very small area there is low shear and that shear has been rising generally in the vicinity.
That may be why 90E does not look as good now as it did a few hours ago, having lost direct overhead support from the high.
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