CSU bi-weekly forecast (Sep 15-28):Above average activity

[clfenwi]

Average ACE for these two weeks is 22.1 units, so the forecast is for more than 28.7 units to be generated.

Igor is the primary factor. "Current forecasts of Igor’s intensity from the National Hurricane Center indicate that this hurricane alone could generate enough ACE to approach the above-average definition." Of course, Julia and Karl will contribute as well. The forecasters also note that several models develop the next wave to come off Africa. As the Madden-Julian Oscillation is expected to remain weak, it was not a singificant factor.

The rapid intensification of Igor caused the last forecast (average activity), to be a miss, bringing their sucess rate down to 33% (1 for 3).

http://hurricane.atmos.colostate.edu/Includes/Documents/Two_Week_Forecasts/september_15_2010.pdf

[cycloneye]

Average ACE for these two weeks is 22.1 units, so the forecast is for more than 28.7 units to be generated.

The two week period started with a boom as Julia went up dramaticly in intensity.I think 28.7 units is reachable.

[KWT]

28.7 isn't just reachable, I'd say there is something like a 95% chance it'll be beaten and maybe a 50% chance we'll end up close to double that when all is said and done...

[clfenwi]

Thanks to Igor's strength and the rapid intensification of Julia and Karl, it took all of three days for this forecast to verify (29.5 units of ACE from 15 0000Z - 17 1800Z).

[KWT]

Now we have to see whether we cxan double it like I suggested is possible, Lisa is starting to chip in with a small amount and we may well have another system developing in the W.Caribbean before the end of the forecast period as well...

[clfenwi]

Just over half-way and by my calculation we're at 44.5675 units for the period. Could get close to a double (57.4 units; twice the above average threshold) if Invest 95 develops and slides north to get some extra time over water.

[supercane]

VERIFICATION OF SEPTEMBER 15 – SEPTEMBER 28, 2010 FORECAST
The two-week forecast of tropical cyclone activity from September 15 – September 28 verified quite well. This forecast was relatively straightforward, since Igor, Julia and Karl were all present at the start of the forecast period, and Igor was expected to generate large levels of ACE given its location and track forecast on September 14. Activity at above-average levels (>130%) was predicted, while observed activity was about 220% of the average during the period, due in large part to Igor’s copious ACE generation. The Main Development Region (MDR) continued to be the primary focus for TC activity. Eight named storms have formed in the MDR so far this year, trailing only 1933 (11) and 1995 (9) for storms forming in the MDR in a single season. Tropical Atlantic vertical shear was very low over the past two weeks, which is a likely reason for why storms continued to form and track through this area (Figure A).
The primary contributor to ACE during the two week period was Igor, with Julia, Karl and Lisa also contributing significant ACE quantities. Matthew generated only a small amount of ACE before making landfall in Nicaragua. The Madden-Julian Oscillation was of a fairly weak magnitude throughout the period and likely did not play much of a role in modulating TC activity (Figure B).