The TC Wind Group help their monthly conference call on 4/10/13 at 11 AM.
Call Participants: Michael Brennan (NHC), Bryce Tyner (North Carolina State University), Reid Hawkins (ILM), Jonathan Blaes (RAH), David Glenn (MHX), John Billet (AKQ), Bob Bright (CHS)
Bryce went over his recent error function analysis for the Holland et al. (2010) interpolated wind speeds. After examining all 219 available H*Wind analysis times, he determined the normalized error for each quadrant as a function of distance from storm center. His analysis shows a large clustering of normalized error as a function of distance from storm center. Based on this clustering, he calculated the average error as a function of distance from storm center. He then applied a four degree polynomial fit to the data using least squares fitting. He did not include data points within the radius of maximum winds in the fit due to data sampling issues within this region. The error function will be subtracted from select tropical cyclone analyses times to show what changes to the wind field result.
After discussing the wind interpolation issues with several of the WFOs, it was also suggested that Bryce develop a similar error function for the modified Rankine vortex interpolated wind field. An error analysis shows a similar pattern as a function of distance from storm center, though the data does not cluster quite as well. The error function developed from the modified Rankine vortex method will also be used to develop an “improved” wind field. Results of the added error function onto the raw modified Rankine Vortex wind fields will also be posted as soon as they are available.
Training slides will be updated based on the recent TC Wind group results and will be circulated among the regional WFOs prior to the start of the tropical cyclone season.
David Glenn has begun analyzing gust factors over the ocean for select buoy stations during Irene (2011). His initial analysis suggests reduced gust factors as distance above the ocean surface increases. In addition, gust factors appear to be below a value of 1.25 for much of these data, much lower than what was seen over land during Irene (2011). When finalized, David will share the results of his analysis via a blog post.
The next TC Wind Group conference call will be held on Wednesday, May 8th at 11 AM.