Real Wx Services has felt the need to revise the preliminary hurricane that was issued earlier. There were several deciding factors that have gone into the revision of the forecast. We will discuss these factors in this update.
On the other side of the coin there are also some wildcards which at this point will be interesting to see what effect they have on the hurricane season.
First factor in favor of a more active hurricane season is the above normal SSTS.
The next factor that seems to be in this seasons favor is the AMO or the Atlantic multidecadal oscillation
Now, this image only goes to 2006 but one thing about the AMO is that its phases last anywhere from 20-40 years which basically means that we are still in a positive phase. And a positive phase of the AMO is a good indicator of hurricane activity being increased and sometimes even doubled from standard activity. As you can see with this graph below..whether the AMO is negative or positive does make a difference in #s and somewhat on tracks as well..
As you can see in the image on the right with a positive AMO the #s are indeed increased versus the figure on the left.
Another factor which is in favor of the hurricane season being more active is the ENSO itself. There is no longer a question of whether the ENSO is going to become neutral but now the question becomes , how long does it remain neutral and where does it go from there? Of course this answer can have an effect on the season as well, if it is only brief at neutral and swings back to an El Nino it would cause lower #s. So this is something to keep in the back of the mind as so far things weather pattern wise are comparable to last seasons weather pattern of wash, rinse and repeat.
There are a few things that also are on the opposite side of the coin that would or could argue for a lower # season.
Over the past 12 years the Southern Hemisphere ACE has correlated quite well to the following Northern Hemisphere ACE & hurricane season. The latest season of the SH ended up with a near normal ACE. This would argue for a near normal NH hurricane season.
People have been comparing this season coming up to a potential season like 2005. The one main difference between that season and now is the ACE.
Truth of the matter is that basically we are at a 30 yr record low # as far as the ACE is concerned and it is starting below normal as well. So this factor here could argue for a normal season.
The other factor against an active hurricane season is the QBO or quasi-biennial oscillation. Atlantic hurricane activity is enhanced during the west phase of the QBO and diminished in the east QBO years.
The following is courtesy of Dave Tolleris or DT.
“
The QBO blows in east or negative phase for several months... sometimes as long as 9 to 15 months... then moves back towards Neutral.... then in the positive phase for 9 to 15 months... then back towards Neutral. The QBO phase ( +QBO or -QBO) influences the amount of High latitude Blocking in the Jet stream... the strength and intensity of the Pacific Jet stream... and African rainfall which is an important aspect of hurricane seasonal forecasting.
As this link shows the current QBO is in the negative or EAST phase and continues to increase in the negative or easterly values as they come out of the winter into the spring. This means that during the spring months we can anticipate the QBO to reach a value of at least -20 at some point over the next few months. The current -QBO has been in the easterly phase for last eight months so the probability is pretty high that the QBO is going to remain in the strong negative phase for several more months.”
So the above is another factor of a season that could end up being either normal or less then normal.
So there are various factors behind the scenes here that could work out for or against this seasons hurricane season.
And even in the Real Wx Service weather team there is a difference of opinions. However…we have basically decided that the things in favor out weigh the things not in favor. However. since we are a team we are issuing a team forecast and it is as follows:
If i were to issue a forecast based solely on my thoughts it would be for 10-12 named storms with 4 of them as major hurricanes. We will continue to monitor things as the season approaches!
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