Atlantic Hurricane Tracks - A Closer Look

[My Weather Today]

No, I'm looking at the dailies that go back to 1950:

ftp://ftp.cpc.ncep.n...1.current.ascii

I looked at the 26 east coast direct hurricane hits (including FL) from 1950 through 2010 that weren't storms that just pretty much grazed the east coast. I counted 19 (72%) with a +NAO and only 7 (28%) with a -NAO on the day of hitting. Three had >+1, seven had +0.5 to +1, nine had 0 to +0.5, four had 0 to -0.5, three had -0.5 to -1, and none had less than -1. The lowest was -0.965 (Hazel of 1954). The avg. and median NAO was ~+0.3. OTOH, The nine grazers averaged near zero with a -1.359 lowest NAO.

So, there clearly seems to be a partial positive correlation of NAO and nongrazing east coast hurricane hits, which makes sense when one considers the tendencies of the overall pattern in the western Atlantic/east coast during a -NAO vs. a +NAO. This all tells me that getting a nongrazing east coast hit from 91L with the projected ~-2 NAO will be very difficult. Even getting a graze wil be pretty hard.

The problem with that data is that it is using the NAO measurement on the day of the storm making a landfall. I would think the NAO phase either a week up to two weeks prior to landfall would be a more useful correlation, correct?

You're bringing up a good point. Actually, one week prior does appear to have a smaller partial correlation while two weeks prior appears to have little, if any, correlation. I count 26 (earlier I had 25 but I had missed one) nongrazing east coast hurricane hits from 1950-2010:

1) Avg. NAO day of hit: +0.3; 19 (73%) had +NAO and 7 (27%) had -NAO.

2) Avg. NAO seven days prior to hit: +0.2; 16 (62%) had +NAO and 10 (38%) had -NAO.

3) Avg. NAO 14 days prior to hit: 0.0 (right at neutral); 14 (54%) had +NAO and 12 (46%) had -NAO.

Seven days earlier, there were actually three with an NAO of less than -1 with the lowest at -1.786 (Cleo of 1964). Regarding 14 days earlier, there was only one below -1 although it was at -2.001 (Cleo of 1964). So, yes, these stats tell me that on occasion the NAO has been solidly negative 7-14 days earlier (3 of the 26 hurricanes). However, the NAO did increase a lot by the day of the hit for these three storms to +0.324 (Carol of 1954),

-.272 (Cleo of 1964), and -0.209 (Inez of 1966.

With the GFS ensemble mean maintaining its NAO prediction near -2 for days 7-10 and considering their recent verifications (also the Euro ensemble has a similar -NAO), it is pretty likely going to verify as a strongly -NAO when 91L would likely be in its critical position north of the Greater Antilles (assuming it doesn't stay in the Caribbean). So, despite the good point you mentioned, this all still tells me the chances of a nongrazing east coast hit are very slim because the NAO is almost definitely still going to be quite negative. Had the NAO forecast for 7-10 days out been for a rise to only slightly negative or greater as opposed to sinking to strongly negative, I wouldn't be using the NAO to make these east coast avoiding predictions for 91L.

So am I interpreting this data correctly...doesn't these results kinda support what am19psu said back on 07/30/11?:

"NAO is kinda chicken and egg... the storm can have a definite effect in its status... I don't think you can just look at NAO progs and make a forecast off it because of the connection to the storm itself...Just that the future cyclone can have a direct effect on NAO state through latent heat release... not to mention other things like pacific convection and mountain torques that are not handled well by the models... I wouldn't use an NAO prog as a basis for my forecast verbatim."

So others won't complain, maybe you (or I if necessary) need to create a separate thread for this research and we can continue this discussion over there, since I know everyone is skimming though here for the latest thoughts on Invest 91L.