Sunday, May 20, 2012

Cyclone forecast a BOM

The 2011-2012 cyclone season came to a close in April. In October last year the Bureau of Meteorology issued its forecast for the 2011-2012 season. ABC provided some coverage (Here and Here)  focusing closely on forecasts for NW Australia. Here's BOM's forecast from last year:


2011-12 Australian Tropical Cyclone Season Outlook


Summary: Above average tropical cyclone activity likely for the Australian region this season
The outlook favours the following scenarios for the coming season:
  • The whole Australian Region has an 80% chance of having more than the long-term average number of cyclones. The long-term average is twelve.
  • The Western Region has a 65% chance of observing above average number of tropical cyclones, where the long-term average is seven.
  • The North-western Sub-region has a 60% chance of above average number of tropical cyclones. The long-term average is five.
  • The Northern Region has a 60% chance of above average number of tropical cyclones, where the long-term average is two or three cyclones.
  • The Eastern Region has a 65% chance of observing above average number of tropical cyclones, where the long-term average is three or four.
Table 1 Forecast values for the 2011/12 Seasonal Outlook for Tropical Cyclones (TCs) for the four main tropical cyclone regions and the north western sub-region.
Region
Chance of above average tropical cyclone activity
Long-term average
Forecast skill
Australian region
80%
12
Very high
Western region
65%
7
Moderate
North-western sub-region
60%
5
Moderate
Eastern region
65%
4
Moderate
Northern region
60%
3
Low





BOM forecast the number of cyclones in all regions should have been above the long term average. It rated its forecast skill as "Very High". How did it play out???? Here's a map showing tracks of cyclones affecting the Australian region for the forecast period based on reports by the Darwin Regional Specialised Meterological Centre (links to monthly reports below).
Figure 1 Cyclone tracks for 2011-2012 cyclone season


Here's a summary table for Australia as a whole and each region:



Table 2 Actual cyclone numbers for the 2011/12 Tropical Cyclone Season. 
Region
Difference from (Average)
Reported Cyclone Numbers
Forecast skill
Australian region
-4 (12) 
8
Poor
Western region
-2 (7)
5
Poor
North-western sub-region
-2 (5)
3
Poor
Eastern region
-2 (4)
2
Poor
Northern region
-2 (3)
1
Poor

Links to monthly BOM reports.
Nov 2011 No Cyclones  in Australian region (5°S-40°S, 90°E-160°E) 
Dec 2012 3 Cyclones in Australian region (5°S-40°S, 90°E-160°E) 0 NW region Alenga, Grant, Fina
Jan 2012 2 Cyclones in Australian region (5°S-40°S, 90°E-160°E) 2 NW region HeidiIggy
Feb 2012 1 Cyclone in Australian region (5°S-40°S, 90°E-160°E) 0 NW region Jasmine
March 2012 2 Cyclones  in Australian region (5°S-40°S, 90°E-160°E) 1 NW region Lua, Koji-Joni
April 2012 0 Cyclones  in Australian region (5°S-40°S, 90°E-160°E) 
Total for season: 8 in Australian region (5°S-40°S, 90°E-160°E) 


Seasonal forecasts are news, but the outcome of those forecasts are news also, especially when the forecast skill is so poor. For the 2011-2012 cyclone season Australia's premier meteorological institute predicted an 80% chance that cyclones would exceed the long term average (12). The actual number of cyclones (8) was 33% below the long term average. Missed it by that much!

Wikipedia also have a post HERE with similar numbers. 

3 comments:

  1. Bob in CastlemaineMay 21, 2012 at 5:04 PM

    Well spotted Marc.
    Just like the UK MET with their repeated way-off BBQ summer predictions, the BOM stays on message to the virtual world of the warmist orthodoxy.
    But statistically the odds are they will one day fluke one correct, and boy won't we hear about it then!

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  2. Good work Marc - over at BOM they're sucked into fear and they like to spread it! They can't even get Perths 7 day forecast right!

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  3. Yes Marc you would think there would be consequences for continual useless forecasting that cost taxpayers hundreds of millions of $'s - but apparently not if you are the BoM and posturing about saving the world from GW.

    ReplyDelete

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