Posted 31 May 2010 - 21:10
I'm personally expecting a pretty big season this year with many factors that have been in play in some of the bigger seasons of the past 50 years or so.
Firstly we have to look at the SSTs. They are currently still running well above average from about 5N upto 25N which means it covers pretty much all of the deep tropics. The Gulf has warmed up and the Caribbean remains very warm as well and the Gulf Stream looks good, though temps near the East coast aren't as warm due to the troughing/90L combo over the last few weeks. Still the temperatures can only be compared with 2005 and the fact we are comparing it to that season is quite a scary prospect. Therefore that is a clearly very explosive signal. EVen if things do cool a touch during the summer, they should remain probably close to if not actually recording the record.
The El nino that was present in the Pacific over the winter has now totally decayed and is starting to get replaced by much colder water with a quick transition towards La Nina. La Nina typically reduces shear and therefore makes long tracking systems more likely when systems develop. I'm currently expecting a borderline weak/moderate La Nina with a range between -0.8C and -1.2C which would put it in about the same range as the La Nina that developed in 2007 and 1998, though the 2007 didn't really develop to that strength till the Autumn. As long as the La Nina doesn't become too potent it should have an effect, though I do think other conditions including the SSTs and other factors probably will play a bigger role this year.
Another factor that is being watched currently is the pressures in the Atlantic basin. The two best long range models (the CFS and the ECM) are both calling for well below average pressure. This is important because it makes it easier for storms to develop and on top of this lower background pressures tend to mean systems will get lower pressures when they strengthen. The 2005 was a classic example of that where the Pacific Monsoonal trough extended eastwards into the Caribbean and Gulf and allowed 3 Hurricanes to break into the top 10 lowest pressure list. Whilst I'm not expecting something quite that extreme, the lower pressures have been present with many of the big recent seasons.
Other smaller factors this year I'm watching is firstly the continuing lower than normal temperatures in the upper Atmosphere. This is important because it increases the lapse rates which help to deepen the convection which is a key factor in helping to develop storms, esp in the formative stages. I'm also expecting a pretty strong wave train this year coming out from Africa with Indian Oceanic temperatures also running well above average which should also help with keeping the SAL down, though I suspect we will have strong outbreaks in July with the ITCZ lifting northwards as systems develop quite quickly, The easterly trades will also stream across should help to provide good condtions aloft in terms of divergence.
If I had to place a highest risk zone I'd suggest the E.Caribbean, The Yucatan south through to Mexico/Central America, the Bahamas upto the Carolinas and the E.Gulf. That being said I think many areas are at much greater risk this season simply because of higher numbers this season.
I suspect a slightly above average June and July with 2-3 storms developing in June and July, with possibly an early Cape Verde type system in July, with a general higher risk than normal of something forming east of 50W at the very least in July. I suspect this will be followed by an explolsive couple of months probably between the 10th August-15th October which could well see a good 12-13NS develop in a 60 day period as conditions look explosive, and even those numbers could quite easily be a little on the low side. I also expect an above average latter part of the season with the maturing La Nina helping to prolong the favourable conditions.
I'll go for a conservative 17/10/5...could be higher if the early season kicks in more than I expect at the moment. If June/July do follow more typical developing moderate La Nina climatology then the NS number could be just a touch lower in the end, but should still be decently above average.
Nick F, on 25 May 2010 - 13:40 , said:
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