The Color of the Weather? Forecasts in the Bahamas

I spent the better part of my careers (all three) evaluating contract proposals. Colors and points were a key part of the process. There are three common forecast providers here (proposers, if you will), the NWS, Worldweatheronline, and BarometerBob. First, thanks is due to all three. Having said that, it’s noticeable that, in the springtime, they generally agree among themselves a scant bit better than 50% of the time. The differences are often significant. This is not about forecast accuracy, just agreement! The following chart expands with clicking. Green is agreement. Yellow is near agreement, Orange is disagreement.

Which One Do We Choose

So how do they score?

If three services have something to say, Agreement is worth 4 pts, near agreement is 2pts and disagreement is 0 pts. If two services have something to say it is 3, 1, and zero. there are a total of 72 points possible.

So what?

The three services most often agree on wind strength — 78% of the time. On wind direction it is 47% and on general conditions 44% Flipping a coin is 50%. Their range of disagreement is between 56-58% meaning no two are significantly parallel. So one has to wrap all three into a meta-forecast (below) that more or less bounds conditions.

The problem is the meta forecast is frequently the kind of information that keeps boats in marinas. The range of uncertainty is significant on 5 of 6 reporting periods. This is one reason we opted to downlink satellite weather information to the boat. Using satellite imagery, winds aloft information, and radar data (even though it doesn’t cover our area, it does show what might be coming) we can begin to pick our providers.

We have found local conditions affect the NWS forecast as land in the area discussed, AMZ117, is a local heating and wind direction wild card. We have found significant disconnects between the general description (Sunny) and the probability of precipitation (92%) from Worldweatheronline. And BarometerBob always seems a bit stormier/blustery (conservative) than conditions observed. It’s like learning the colors of water. One has to learn the colors of forecasts.

Meta-forecast example. Orange depicts too wide a range of variable.

TUESDAY S – WSW 4 to 15 SUNNY or T-STORMS Hunker
Down?
TUE
NIGHT
SE -NW 2 to 10 PC Anchorage
Choice?
WED ENE – S 4 to 13 SUNNY – PC Anchorage
Choice?
WED
NIGHT
W – SSW 5 to 22 PATCHY RAIN or TSTORMS Hunker
Down?
THU NW – N 10 to 22 SUNNY – PC
FRI NE – S 4 to 17 PC – OC Anchorage
Choice?

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