Friday, 19 April 2013

2013 Hurricane Season Outlook

Welcome to my 2013 hurricane outlook. This year will be a challenge for forecasters as we have a neutral ENSO state, moderation in the -PDO and warm AMO pattern.  Lets get right into my analog package.
Top 3 Analogs 

The top year I have been looking into is 2003 which had a weak el nino summer and a warm AMO. The 500mb pattern in the summer featured a trough in the east and a ridge in the west which is what I am expecting this summer. The european is consistent with this type of pattern setting up. Notice the cluster of tracks east of florida and in the western gulf.
1996 is my second best match which had a weakening moderate la nina, similar to this year. It also had eastern troughiness in the JJA 500mb pattern. We also see the spray of tracks originating off of Africa and spreading towards the eastern caribbean and carolinas. This was another active year along the eastern seaboard with a +AMO pattern.
1952 has a nice ENSO match with a similar spread of tracks. Several systems may have went unnoticed in the North Atlantic with the lack of satellite data.
Here is my full analog package SST blend:

If we compare it to this year, notice the similarities with the cool western gulf and warm AMO tripole. There is also cool water in nino 1 and 2.

ENSO will be a very key driver for this years hurricane season. The european and canadian guidance suggest a weak modiki el nino throughout the summer with dryness around florida/cuba. The euro monthlies has a trough over the great lakes with a near normal hurricane season in the atlantic basin. It is suggesting two spreads of tracks, one extending from the MDR towards the gulf states and a second one along the eastern seaboard late in the season. Given the overall pattern in place, I agree with the overall tracks advertised by the european but disagree on ENSO state. Currently, we have an area of warmer then normal subsurface SST anomalies between 140E and the dateline. These anomalies may make an attempt to upwell in the central ENSO regions but in a modified form. 

We continue to see OLR anomalies clustering around the maritime continent/eastern IO which supports a neutral ENSO/weak la nina pattern. The atmosphere is not headed towards an el nino very quickly given the lack of a strong subsurface warmth which.

Mid tropospheric easterlies west of the date line and subsequent SOI rises will prevent an incoming el nino. A la nada or very weak el nino is what I am expecting by late summer. This should not prohibit hurricane development given the lag effect involved with a changeable ENSO state. With this being said, we need to look at other factors that can influence the hurricane season.


Currently we are experiencing a downwelling easterly QBO state which should strengthen into a westerly state by the summer. A downwelling easterly QBO will help promote easterly winds in the stratosphere with lower heights over the caribbean and an increased hurricane threat in the atlantic basin this summer. Notice how the easterlies are already beginning to strengthen in the subtropics around 50mb which is consistent with my analogs (1964 and 1969).
Hurricane Track Forecast

Within a positive AMO period we should always be on the lookout for hurricane tracks up the eastern seaboard. I think this year will be no different with several threats from the carolinas to New England and towards the eastern caribbean. Several of my analog years are pointing towards east coast storm tracks such as Isabel, Juan, Fran and Dora. Many systems may end up tracking just to the east of the northeast coast. In august and september several central caribbean and gulf of mexico tracks are likely as storms shift southwestwards and the bermuda high weakens. Florida will be in the middle of this  track spread which means that it is also at risk of several land falls. I don't feel as if this is a hurricane season like 2005 or 2004 but an above normal season is in the works with a -NAO likely this may with a build up of warm SST's in the MDR.