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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On the 20th of May (thursday)
I agree that BP has been BS'ing long enough. The oil is gushing out much faster than BP is telling.
I made it to Abilene, Texas yesterday. Hoping to chase a little today, not a great chance of storms, but should be fun.
any thought on the severe potential around wednesday?
Good morning Ike! The thing that has me surprised is what "I" see as government complicity in the artificially low numbers. The entity with the most to lose, is the one providing the numbers that our government is offering for public digestion. Again, I feel the President has to the power to make a LOT of corrections in past policies and move forward with tighter regulations, and a VIABLE alternative energy policy. He has the political coin to make a lot of things better and safer, I hope he uses it wisely.
I'm not an expert...I'll take what they're saying about it and agree.
The oil spill is going to cause even more problems I feel.
They need to get it stopped. Maybe what they're doing now will work.
Blog Update
Weak tropical disturbance is expected to develop later this weekend; Eyjafjallajökull continues to erupt
Conditions in Trinidad are sunny, hot (already) and pretty still. Scattered cloud and haze.
The wave east of here is still trying to force its way through a "wind wall" of strong north-easterly flow that is blowing the thing away.
Still hope to get some showers but I may have to wash my car to guarantee that....
Yes that 1006 MB low in the southwest Caribbean is the wave to the east of Trinidad and Tobago. The 00z CMC shows the same solution. I think that it will develop to possibly a TD once it gets to the SW Caribbean but a band of high shear lies to the north of it, so not too much development there.
00z GFS 180 Hours
Pottery you having the calm before the storm this morning?
Taco :o)
Yep! I truly expect the storm to come, sometime before December. LOL
Wednesday is modeled as a typical lee-trough system over the southern plains. A surface low near SW KS and a dryline extending S along the western OK border.
Looks good except the mid-level part of the system appears on the weak side per the models and the SPC. 30 knots bulk shear/LLJ on the order of 25-30 knots also. Still should see a storm or two worth chasing.
You are so Funny LMBO@ you
Taco :o)
I should be in position to chase in that area, thanks!
I will be starting around Joplin MO and work
my way around then..... I do hope I get to
see some storms too....
Taco :o)
where are you now?
Can't help you with the forecast, but after watching the near accident that OZ almost had on the highway the other day, I think you chase guys need to get yourselves a bigger chase vehicle. I found one for you, but you may need to reconfigure the front end design a little. :)
yea
I'm in Mobile AL right now I have to work this week.
My Vacation will start on Saturday and will be there
Saturday night to see my Mom.
Then on Monday the 25th the chase will be on...
Taco :o)
haha thats awesome!
Oh ok, I drove through the Joplin area yesterday, I have family just north of Springfield
see you later
aqui hay elecciones... y es la primera ves que voy a votar
Still partly cloudy here, but so far no actual rain. I'm sure that'll change before the week is out. Meanwhile I'm enjoying the last of the high-induced tropical breezes before the summer humidity sets in....
Still watching that Twave near Guyana prove that conditions are not yet conducive to TC development.... maybe next weekend (and I'm thinking maybe a td at most).
I'll be in and out today.... got some work related computer work to do, but have to get that done before I can lounge around the blog.
L8r......
Yea I went last year, a week earlier and did not even see a thunder cloud. I came back home just in time to see the 'NonTropical Storm"
come across Dauphin Island AL....
Taco :o)
dang, well Ive already driven through a couple storms on my way here, good sign hopefully
The 1502 Hurricane of the Dominican Republic: Columbus’ Hurricane
And probably associated with a bit of a speed max at 500mb from a weak mid level shortwave that is over the TX panhandle and nosing into western OK (on water vapor loop). Activity would favor the southern edge of this feature as it moves east/ENE. Probably responsible for the current convection near the Big Bend area of TX.
So, put that together with the boundary and we might see some storms form up near the ARLATX this afternoon.
He's been in here just a little lately. Prolly just still on break...
*Pretty sure I saw him in here for a post or 2 a couple of weeks back*
So I'm in a good position in Abilene then?
http://www.nytimes.com/2010/05/16/us/16oil.html?hp
"Giant Plumes of Oil Found Forming Under Gulf of Mexico"
He moved from Key West to Port St. Lucie a while back and became kinna scarce. He popped in last week if memory serves.. I like the lad and feel he has potential in the weather forecast arena.
Only the GFS is showing development. What the other models show with a single closed isobar and a "L" is a broad area of low pressure.
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