Grib Files - Low Wind Speeds for Hurricane Mathew

[SF Bay Dude]

I've never had the use of downloadable grib files on my adventures, but the next one will, no doubt. I've been playing with gribs now for about 6 months now, getting used to the forecasts vs reality, but when I look at what GFS is throwing out for hurricane Matthew, it seems like a pretty big gap between what's really happening vs modeling. I am getting 70 knots sustained from the files, when winds are actually recorded and in the range of 120 knots sustained.

I know gribs are always on the lower end of what is actually felt (typically), but this seems like poor modeling and pretty damn dangerous. I get that they are part of the overall toolkit of weather routing and decision making, but still...

[zeehag]

i follow storm 2k, a very accurate cane lovers site. i learn a lot and get to see beautiful pix and all the models of each storm with circles and arrows and a paragraph on the back. they also know when rapid intensification occurs, which other sites fail to pick up.... i noticed that. when compared to reality, s2k has it together. they tell me i'm-a gonna die--we get patricia. so..
matthew r i'd off colombia, yet many sources donot acknowledge that small fact.; follow nhc for htis one. per my gurus advices and see how it goes. the 3 day out predictions are not accurate due to the conditions
nc cat 3
bahamas cat 4 unless the formation r i's again..it has stalled some..

[Jim Cate]

Originally Posted by SF Bay Dude

I've never had the use of downloadable grib files on my adventures, but the next one will, no doubt. I've been playing with gribs now for about 6 months now, getting used to the forecasts vs reality, but when I look at what GFS is throwing out for hurricane Matthew, it seems like a pretty big gap between what's really happening vs modeling. I am getting 70 knots sustained from the files, when winds are actually recorded and in the range of 120 knots sustained.

I know gribs are always on the lower end of what is actually felt (typically), but this seems like poor modeling and pretty damn dangerous. I get that they are part of the overall toolkit of weather routing and decision making, but still...

I dunno where you get your gribs from, but each time I subscribe to download them via Winlink and Saildocs, the first chart comes with a lengthy disclaimer about the shortcomings of GFS gribs. One of the caveats specifically mentions that they do not do a good job of analyzing tropical storms (including hurricanes). That this is true should now be apparent to you!

Jim

[leftbrainstuff]

'All models are wrong but some are useful.'

Weather forecasting correlates best when conditions are largely steady state.



Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[SF Bay Dude]

Originally Posted by Jim Cate

I dunno where you get your gribs from, but each time I subscribe to download them via Winlink and Saildocs, the first chart comes with a lengthy disclaimer about the shortcomings of GFS gribs. One of the caveats specifically mentions that they do not do a good job of analyzing tropical storms (including hurricanes). That this is true should now be apparent to you!

Jim

I've been using Luckgrib and get them directly ingested from my wifi since I am still on land. I just open the app, select my zone and parameters, and it's there for me. There's no disclaimer. Yes, very apparent, or true? Depends on whether I am going to weather. Oh!

Joking aside, them not doing a "good job" is the understatement of the year.

[JPA Cate]

The Gribs do have limitations, as does hurricane track predicting. What we are not yet able to do is ACCURACY.

all week, zeehag has been posting data from various sources, and recommending you check the National Hurricane Center for what she considers the most reliable track predictor. They, too, got some of the strengths wrong. The water's quite warm where Matthew is now.

Since the track prediction is so difficult, and the further out in the future the more it can vary, when the water is hot and it is hurricane season, that if you have a boat you want to protect, you prepare for the worst expected outcome. If it comes weaker to you than predicted, that's a blessing, but not to be counted on.

Another factor is that all the predictions are for average sustained winds, like over 10 minutes, but a call to the outfit will tell you how long the averaging is. Gusts can be up to 50% higher, often 40% higher than the averages you are given. The force on the boats goes up as the wind speed, squared (times itself).

Ann

[zeehag]

reported from haiti via friend ham: on the ground les cayes .. flooded winds 104. general hospital flooded. wind now starting to rev up. 82 steady now with gusts to 107 and ramping.

track for fla showing cat 4 to ga then weaken to c3
dayumm. r i p fla.
was nice to have known ye.
guess momma nature is pissed at ye for some reason.
i hope y'alls are ready, mon.
and i hope it aint the bastid it is spozed to be.
wont know where it will actually go until after cuba. this new update sucks for fla and all islands between haiti n maine
north of chessy is still unknown

[jmschmidt]

Don't forget that commercial weather broadcasts usually quote statute miles per hour for winds. So unless you are looking at marine, aviation or military forecasts, which are in knots, there is a seeming discrepancy.

[classic1899]

thought this post was about grib file accuracy instead we get zeehag rambling on about Mathew in some weird wanna be pirate baby talk not sure what that's about.
anyway
i have used gribs for years now but have given up paying much attention to speed. However i do find the direction quite useful and speed i simplify into light, moderate, strong etc.
if its a storm or a good blow they are always way under actual wind speed

[Littlechay]

Originally Posted by Ann T. Cate

Another factor is that all the predictions are for average sustained winds, like over 10 minutes, but a call to the outfit will tell you how long the averaging is. Gusts can be up to 50% higher, often 40% higher than the averages you are given.

I think I am correct in stating that the US averages sustained winds over one minute. In steady winds this won't make much difference but in gusty conditions it can make a lot of difference.

I have been in winds over 100 knots quite a few times but never been in a tropical cyclone (hurricane) so I don't know how gust they are when you are in the peak wind areas.