There has been a change in the analysis of sea-surface temperatures used in the RUC. The RUC (and the Eta) have been using a hi-res NESDIS product (on a 50-km grid), while the AVN and NGM use a 1 degree by 1 degree product known as the Reynolds analysis. In the past couple of weeks, differences between the two analyses of up to 10 degrees Celsius(!) have been noted over the Gulf Stream, and the Ocean Modeling Branch of NCEP/EMC believes that the Reynolds analysis is closer to the truth. The very warm waters in the NESDIS product have, we believe, led to overdevelopment of east coast cyclones by the Eta.

 While NESDIS assesses possible problems with their analysis, both the Eta and the RUC are going to return to using the Reynolds SST analysis. The change in the RUC was implemented at 18Z on Wednesday 20 December 2000. A comparison of the two SST analyses can be found at http://www.emc.ncep.noaa.gov/mmb/ruc2/sst.html

 Note that the hi-res analysis file also contained high-resolution Great Lakes temperatures provided by the Great Lakes Environmental Research Laboratory. It was not possible to separate these from the NESDIS ocean temperatures, so this Great Lakes data (which seems to CORRECTLY analyze warmer Great Lakes temperatures) will not be going into the RUC (or Eta) as long as the Reynolds analysis is used. I will inform the forum when/if we return to using the NESDIS product.