Record Atlantic SSTs continue in the hurricane Main Development Region
Sea Surface Temperatures (SSTs) in the Atlantic's Main Development Region for hurricanes had their warmest April 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 area 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 1.46°C above average during April. This is the third straight record warm month, and the warmest anomaly measured for any month--by a remarkable 0.2°C. The previous record warmest anomalies for the Atlantic MDR were set in June 2005 and March 2010, at 1.26°C.
Figure 1. The departure of sea surface temperature (SST) from average for May 13, 2010. Image credit: NOAA/NESDIS.
What is responsible for the high SSTs?
As I explained in detail in a 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. Negative AO/NAO conditions have been dominant much of this spring as well, resulting in further anomalous heating of the MDR waters. 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, the warmest on record in March, and will likely be classified as the warmest or second warmest on record for April, since NASA just classified April as the warmest April on record for the globe. 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 April SST anomaly does not bode well for the coming hurricane season. The three past seasons with record warm April SST anomalies all had abnormally high numbers of intense hurricanes. Past hurricane seasons that had high March SST anomalies include 1969 (0.90°C anomaly), 2005 (1.19°C anomaly), and 1958 (0.97°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.
The SSTs are already as warm as we normally see in July between Africa and the Caribbean, and we have a very July-like tropical wave approaching the Lesser Antilles Islands this weekend. However, wind shear is still seasonably high, and the tropical waves coming off of Africa are still too far south to have much of a chance of developing. The GFS model is indicating that shear will start to drop over the Caribbean the last week of May, so we may have to be on the watch for tropical storms forming in the Caribbean then.
For those of you interested in a more detailed look at the early season tropical weather outlook, consult the excellent wunderblogs of StormW and Weather456. I'll be back with a new post on Monday.
Jeff Masters
Reader Comments
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Good morning Tampa, it's a beautiful, sunny, humid, late spring day in Arlington, TX.
It's about 80F, light E winds at 5-10MPH, RH about 65%. Prime conditions for our area of instability in the TX Panhandle to move SE and wreak havoc, with strong 70-80MPH straight-line winds in NW TX!
Looking at the NOGAPS, GFS, EURO.. Hey, I'm not crying out development as some are here. Just saying a broad tropical, sheared low pressue system looks likely. I don't understand why weather scholars have to be soo stuck up. Don't turn out like scottsvb please. He almost caused me not want to be a meteorologist.
day 3 severe oak in the zone again
Morning all. Miss E looks upset.
Hi Weather456, thats all I've been saying, nothing big yet unless the shear decreases.
No one owns the corner market on disasters. All disasters are horrible no matter what form they come in. To say one is less or more than another is in itself the true form of idiocy.
That is a dang large amount of Ash pumping out now.......Redoubt didn't erupt that large i don't believe.......Is this the largest blast thus far?
i did not recognize you
yeah but its not ever gonna change. I already hear people saying if the oil comes it might be a good opportunity to get some beach front at a decent price.,
Most the models had it out to sea yesterday..gfs had it far away from the NE. Trend has been more land affected & stronger. Looking at the different parts pulling together, I've liked the center going up the coast or even leaning toward a little more land all along. If it sucks in the energy east of FL, it should be memorable for someone. I'm only at 45% we'll see storm reports & an event of sorts. No surprise the local news isn't hyping more than rain. It's a few days out yet..
Yes, wow.
With ENSO first, SSTs is the 2nd largest modulator of season activity.
It is likely 16 named storms maybe the lower end.
I suspect noaa will be conservative but will not ignore those SSTs.
Try political chicanery at the ArmyCorps of Engineers. The contractor who built the section which collapsed told them in written&archived complaints that the soil hadn't been properly compacted, and was threatened with a breach-of-contract lawsuit if he failed to proceed with the work. Then his company went bankrupt exceeding the building requirements set in the terms of his contract.
Katrina itself didn't even come close to overtopping the levee at that section.
Did you somehow miss the massive wall of text that pat posted? NOLA is there because it needs to be. Can more be done to lessen the risk of major storms hitting it? Absolutely. Look at the Netherlands - this is a case of an entire country nearly at as much at risk as a single city, and yet they persevere, through a system of massive seawalls and IMO, the best water control features in the world. The one thing they don't have is ~20 miles of wetlands (depeleted, yes, but not gone) protecting them as well. If they can do it, we can to; it would not be impossible to ring the entire city of New Orleans with a 30 foot earthen levee, topped by concrete - and the Brits are considering a new Thames Barrier, nearly 10 miles across, to protect London. There is talk about the mighty Mississippi - but even that grand river can be controlled and rerouted if the neccessity is needed.
Civil engineering is not about what we CAN do, as we can build just about anything with concrete and steel; it's about how much money we can throw at the problem. Eventually, there will be a point where the survival of the city depends purely on human infrastructure, and even though that will cost a huge amount of money, well, as I said, NOLA is there because it needs to be.
My mother is from New Orleans - and though I've never been, seeing her tears at the devastation (yes, devastation) caused by Katrina converted me to her way of thought. It isn't just the port, or the french quarter, or downtown - it is a city that time forget, a place that holds true the ideals of a past time, and a place whose future rests squarely on the shoulders of technology and the willpower of those who will always remain there.
You hit the nail on the head with that one. LOL.
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