Early 2010 Hurricane Season Ideas
A lot of talk has been going around about what the 2010 hurricane season will entail, well from my point of veiw I see many aspects that are condusive for a busy season however it is still too early to have much confidence about this season.Still here is a very brief rundown of what is emerging at the moment and what needs to be watched...1: SSTA'sThe Sea surface temperatures and thier anomalies are one of the most important factors in the hurricane season and making a call. For now they are well above normal. Interestingly something that has been noted is the SST's in the tropical E.Atlantic during Spring can give a good indication as to how busy a season will be. The E.Atlantic has become very warm which is obviously something thats sparking my interest. I'll do a sperate blog about this another time...2: Spring AO/NAOThis may not be something that you'd be thinking about but it links in very much to the first point. This is because typically a -ve NAO means a weaker Azores High and a -ve AO will mean a southerly tracking jet stream. A weaker subtropical high belt will allow for warming in the Atlantic. It is therefore hardly surprising the SST's are as warm as they are in the Atlantic, given the strength of the -ve AO/NAO this season, if we get any decent -ve bursts in the Spring, expect the SST's to challenge 2005 in the Spring...3: Sahal RainfallWhilst this is not a massivly important factor, when put in tandem with other factors it can make a difference. This is because if the Sahal region is experiencing higher rainfall its usually a good indication that conditions later in the season wil lbe condusive for systems in the tropical Atlantic.4: Tropical Stratopsheric conditionsMuch like the above, its not a massivly important factor apart from in the Autumn where the gradients between the upper air and the SST's start to increase. However it is another factor that can help out to get powerful hurricanes, and is also a more important factor for NE Atlantic systems, almost as much as SSTs.5: Position of the ITCZThis is the belt of convective acitivty that stretches across the globe. If this is further south then normal it tends to suggest there will be less convective structures in a favourable position to develop, though it can also allow more systems to get further west, and obviously vice versa.6: MJO timingsThis is a factor that is probably my weakest point, whilst this factor dosn't usually determine seasons overall activity, the MJO phase gives a very good idea about the timings of upticks of activity. This is because there tend to be dry and wet phases in the tropics, and obviously 'dry' phases will tend to surpress convective development and the other way round for the wet phase. Obviously this isn't the be all and end all and systems will still develop/not develop in both phases but it does tend to give a very good idea...of course this factor needs a very good grip on the tropics, something I'd guess GP would be well versed in!7: Pressure anomaliesThis is a very good indicator of how a season will end up evolving. This is because if you have lower then normal pressure to begin with it will be easier for a system to get going, whilst obviously it will be the other way round if you have higher then normal pressure. 2009 was an example where we had higher then normal pressure which also caused a lot of dry air in the Atlantic, whilst 2005 had well below normal pressures, esp in the Caribbean and Gulf, no surprise therefore we saw so many major hurricanes in that region that season.8: ENSO signalThis is quite probably one of the strongest signals for how a season will pan out. This is because El Nino will generally tend to cause shear in the Atlantic, esp in the Caribbean and Gulf. Neutral seasons tend to be quite active in warm phase cycle summers and La Nina's also tend to be active. It is worth noting however that in some cases a weak El nino is not a curse when it comes to activity, esp if the El nino sets up far enough west which deflects the higher shear into the E.Pacific, like we saw in 2004 and quite possibly in 1969. So these are general pointers to look out for, however what state are we in now....SST's are well above normal throughout the basin...Jan came in 3rd warmest ever and Feb maybe even higher. The gulf is cold but that is more due to the cold US winter, any prolonged period will see the SST's shot up. The general -ve NAO we've had this winter has helped to keep the SST's high as well. Typically the SST anomalies will not change greatly during Spring though obviously large scale changes will make a difference. Typically in the warm phase what you have in March in terms of anomalies tends to carry through to the summer, interestingly last year was an exception due to the big switch in ENSO states.The ECM pressure forecasts also raise my interest greatly as well. They suggest decently below normal pressure across a decent chunk of the tropical Atlantic, focused on the Caribbean region. The main reason this interests me is this is exactly what also occur in 2005, therefore needs to be watched, however of course that can all change.The big uncertainty right now is going to be the ENSO signal, typically you find active seasons become very unlikely above 0.7C however that is not a solid link. The models are quite keen to decay the El nino rapidly during the Spring, the ECM was very agressive indeed in its Feb forecast giving La Nina conditions, however I strongly suspect thats over the top in a big way and over-reacting to the big drop in late Jan.I suspect therefore we will end up between 0.3-0.7C, so borderline El nino/Neutral, however the models aren't always that great when it comes to forecasting ENSO, esp in Spring where there is a lot of change anyway occuring in the global patterns.So at the moment I'd be happy to call an above average season, from the data/forecasts I've seen, however with the added warning that a lot of these factors have time to shift and change...for example the El Nino could stay wher eit is now and not weaken much, the stratosphere temps could rocket, we could see a strong Azores high build in late spring/early summer and cause an uptick in the trades and also a big surge of dry air from Africa and also for pressure to be much higher then forecasted and before you know it your looking at a below normal season...However for now, I see nothing that is going to prevent a busy season apart from the El Nino taking longer to be gone!