68 kt winds over MS oil platform?

[ftolmsteen]

5am this morning 2 readings show a 62kt and a 68 kt wind speed on 42363 (mississippi canyon platform). False reading perhaps or real?

http://www.ndbc.noaa.gov/station_page.php?station=42363

[Dionne]

I believe the reading. Notice it coincides with the pressure drop. It can be miserable in the GOM this time of year. Last December we made the mistake of taking a cruise out of NOLA into the GOM.....headed towards Mexico. The winds were relentless.

[wxman57]

Having been an offshore marine forecaster for 30 years now, specializing in the Gulf of Mexico, I would say that the reading looks good. Note a couple of things. First of all, the anemometer height on the Shell Mars platform is about 400 feet above the surface at the top of the derrick. Winds that high are always a good bit stronger than at the surface (10m/30ft standard height).

Second, the platform sits in relatively warm water (about 70-72F now, just looking at the air temp). I've seen some VERY strong winds with frontal passages offshore during this time of year. What happens is that the cold air really accelerates over the warm water (called a supergeostrophic wind). It's quite common for a cold front that's producing sustained wind of 20-25 kts inland to produce twice that (or more) over the water, with higher gusts. So winds of 50-60 kts with higher gusts are fairly typical with a moderate cold front moving out over relatively warm water. Add to that the anemometer height of 122m/400ft, and you have 68kt winds.

Finally, note that the wind gusts occurred just as the cold front moved through and the wind shifted directions.

Oh, and one other tidbit. This platform's automated instruments measured sustained 70-80 kt winds for 2-3 hours as Ida passed through Mississippi Canyon (before both wind sensors were blown away). I have the 1-second wind recordings from Ida's passage. We sent them to James Franklin and Lixion Avila (doing Ida's post storm). After using Franklin's conversion factor to sea level and converting to a 1-min average, we got 65-75 kt winds for Ida's passage. Based on this, the NHC will likely reclassify Ida as a hurricane from about 18Z-23Z Nov. 9th as it passed through Mississippi Canyon.

[MGC]

Interesting info on Ida there 57.....so, Ida did reintensify to a hurricane. Didn't the NHC discard the recon report of hurricane force winds as a localized event?.....MGC

[wxman57]

Interesting info on Ida there 57.....so, Ida did reintensify to a hurricane. Didn't the NHC discard the recon report of hurricane force winds as a localized event?.....MGC

I talked to James Franklin about that report. They had discounted the report but it turns out that the report was very close to where the platform reported the 80-100 kt winds and nearly at the same time. So it turns out that the recon report may have been correct. Look for a change in the best track data to indicate that Ida re-intensified to a hurricane just SE of LA prior to falling apart before landfall.