Dr. Klotzbach 2009 Season August 4th Update

[clfenwi]

Their SST methodologies are different in two ways. One is the areas used, while they border each other, they do not overlap:


Also, the Colorado State forecast uses observed June-July SSTs while Tropical Storm Risk uses forecasted August-September temps.

[lonelymike]

Any way to forecast the steering currents for Aug-September? I know its hard to get specific more than a week or so out but is there a way to discern an educated guess about a pattern?

[wxman57]

This report seems to place much more emphasis on El Nino vs. the Atlantic Basin SSTs. It will be interesting to see which way the season goes, esp. now that El Nino is actually a little weaker than a few weeks ago.

Unfavorable wind shear will always trump warm SSTs. But it's not just El Nino that will produce the increased shear. Long-range models (European) are still predicting that the Bermuda High will be a good bit stronger than normal in August/September, resulting in higher pressures across the deep tropics and increased trades.

[cycloneye]

Unfavorable wind shear will always trump warm SSTs. But it's not just El Nino that will produce the increased shear. Long-range models (European) are still predicting that the Bermuda High will be a good bit stronger than normal in August/September, resulting in higher pressures across the deep tropics and increased trades.

I saw recently a forecast for NAO (Northern Atlantic Occilation) at the WU site that showed negative NAO in September,meaning high pressure retreats more to the NE and is not strong allowing for warmer ssts as less upwelling occurs and causing pressures to be lower than average.

[cycloneye]

Colorado State University 15 day forecast=August 6-20

The CSU 15 day forecast came out today showing nothing to develop.

http://hurricane.atmos.colostate.edu/In ... 5_2009.pdf

[Stormcenter]

This is all great news for those folks (me included) who went through Gustav and Ike last season not to mention the Katrina/Rita survivors. Let's hope if something finally does get cooking (and more then likely it will) it either is not much or just stays away from populated areas.

[clfenwi]

Looks like the forecast of ACE<6 for the period of August 6-20 is in danger of busting.

[AnnularCane]

Colorado State University 15 day forecast=August 6-20

The CSU 15 day forecast came out today showing nothing to develop.

http://hurricane.atmos.colostate.edu/In ... 5_2009.pdf

So much for that!

[KWT]

Yep it does look like the ACE forecast may bust, depends on whether TD3 can become a hurricane probably as to how bad it does bust.

[clfenwi]

Crunching the numbers for real (rather than roughly guessing in my head), it's almost certain that the forecast will bust as two storms maintaining 40 knots the rest of the way would put ACE above six. Or, if one storm were to die now, the other maintaining 55 knots for the period would do it (and remember, because of how ACE is calculated using the squares of wind speeds, a period of 75 knot winds more than makes up for a period of 35 knot winds). They should be able to avoid a truly spectacular bust (where ACE is above average for the period, > 11.7), but they could come close if one of these storms were to rapidly intensify.

[KWT]

Yeah if Bill does become a major for the last 2 days (which is possible) then its going to come close.

[cycloneye]

Wow,bust bigtime.Below is the forecast from the 6th to the 20th.

Forecast
We believe that the next fifteen days will be characterized by activity at below-average levels. This is due to a combination of factors including a currently very quiet tropical Atlantic and the lack of tropical cyclogenesis forecast by the various global models. In addition, the MJO is judged to be in an unfavorable mode for Atlantic tropical formation for most of the forecast period. Average activity for the August 6 – August 20 period over the years from 1950-2000 and the forecast for 2009 are displayed in Table 2. Figure 1 displays the tracks that tropical cyclones have taken during the period from August 6-20 for the years from 1950-2008. Figure 2 displays the August 6-20 forecast period with respect to climatology. The average hurricane season tends to pick up quite rapidly towards the end of the forecast period.

[KWT]

Well it all depends on Bill now as to whether we get an above average ACE for the period (need a total of 11.7) its certainly probable but we shall see...come on Bill, harry up with becoming a major hurricane!

[clfenwi]

With Bill becoming and staying a major hurricane, the August 5-20 forecast did bust in epic fashion. Remarks from their verification:

The 15-day forecast of tropical cyclone activity between August 6 – August 20 did not verify well. Activity at below-average levels was predicted, while observed activity was at above-average levels. Table A displays predicted and observed activity over the 15-day period. The primary reason why we believe activity was heightened during the 15-day period was due to the fact that the Madden-Julian Oscillation (MJO) increased in amplitude and intensified over the Indian Ocean towards the end of the period (Figure A). This MJO state is typically favorable for tropical cyclone activity in the Atlantic. The intensification of the MJO and development in the Indian Ocean was hinted at by a few GFS ensemble members. We based our 15-day forecast more on extrapolation of the MJO (e.g., coherent eastward propagation from Phase 6 to Phase 7) than on the GFS ensemble, and therefore we under-forecast activity considerably.

In their forecast for August 21-September 4, they are forecasting above average activity (ACE > 27). Part of this, of course, is due to the continued existence of Bill, which they expect to generate another 10-15 units of ACE. They also cite models hinting at development in the first week of the forecast period and a favorable phase of the MJO for the Atlantic.

Ref: COLORADO STATE UNIVERSITY FORECAST OF ATLANTIC HURRICANE ACTIVITY FROM AUGUST 21 – SEPTEMBER 4, 2009

[clfenwi]

Well, by my calculation, Bill generated 9.8 units of ACE in the current 15 day forecast period, just slightly below the low end of the team's expectations. As such, there needs to be another 17.2 units of ACE generated between now and September 4 for the forecast to verify. If Invest 93L were to develop, it would probably be good for a couple of points, with the balance managably being covered by one good long-lived storm. I'd say the forecast is in decent shape so far.

[clfenwi]

Blending Danny's best track with the forecast, it looks like he's going to end up contributing ~4 units of ACE, which would leave 13 units to be generated between now and September 4 for the forecast to verify. It could get spicy if 94L doesn't develop in a timely fashion, but right now it would appear my assessment in the previous post that the forecast is in decent shape remains valid.

[clfenwi]

With Danny and 94L/Erica being shorter lived and less ACE contributive than advertised, it looks like another big bust for the CSU two week forecast. It seems that even with Bill being around for part of the forecast period, ACE was below average (<70% of normal=14.7) for the 15 days. Forecast for September 5-19 comes out tomorrow. They should take climo this time; can't "double bust" that way.

[cycloneye]

15 day forecast from September 4 to September 19

Below average activity for the next 15 days the Colorado State University folks are forecasting.They cite not favorable mjo in the period as the main culprit followed by El Nino.

http://hurricane.atmos.colostate.edu/In ... 4_2009.pdf

[wxman57]

I think the forecast values are missing from all the tables in that report.

[clfenwi]

Remember that ACE is the only quantity being predicted in these two week forecasts, so the blocks for forecast Named Storms, Named Storm Days, etc. are going to be blank.

Forecast is for below normal (<70% climo) ACE. Climo is 27, so the forecast is for ACE<19.