As the Mid-Atlantic and New England gear up for another coastal storm, I finally got around to putting together an animation of Sandy’s visit to the Mid-Atlantic with the Hydrometeorological Prediction Center (HPC) surface analyses overlaid. The animation runs hourly from 10/26/12 to 10/31/12 using the GOES-Sounder RGB Air Mass product. Notice how Sandy changes form a few times while off the East Coast before making that hard left into southern NJ.
I have included a few specific time stamps below to highlight the features that led to this explosive transition from a hurricane to a “superstorm”. Please refer to previous posts to follow how downstream blocking led to the hard left turn.
The image above is from the early morning of 10/28/12 when Sandy (a Category 1 hurricane) was moving east of North Carolina. There was still evidence of a hybrid structure as the area highlighted in red shows drying between ~500 and 300 mb most likely associated with some stratospheric air. All this proves is that Sandy was not in an ideal “tropical” environment at this time. I hope to pull some AIRS ozone retrievals in the coming days to further prove this point. The area highlighted in yellow is the upper-level system that was diving southeast to capture Sandy.
In the early morning hours of 10/29/12, Sandy is surrounded by more green-shading than the previous 24 hours, which would indicate that the storm acquired more of a tropical characteristic as it crossed the Gulf Stream. The relative lack of red-coloring in the near-storm environment suggests that the stratospheric drying had relaxed as deeper energy positioned itself west-southwest of Sandy. The red-highlighted area is the aforementioned upper-level system that had dropped through the Midwest and now looks more stretched out as the stratopsheric intrusion strengthened. This helped to pull Sandy’s outflow west as noted by the cloud shield extending into Michigan at this time. Although not shown in this image, the highest winds are occurring in the southwest quadrant of Sandy, just north of the red-coloring of the stratospheric drying.
This final image coincides with the highest wind gusts observed during the entire event and is three hours after landfall near Atlantic City, NJ. Notice how robust the red-coloring has gotten (in the red highlighted area). The leading edge of this very significant stratospheric intrusion is moving into Long Island, Southern New England, and the northern NJ coastline. The highest wind gusts appear to have occurred just prior to this image and it could have been influenced by the rapidly descending dry air helping to transport high moment air or gusty winds to the surface. The highest wind gusts experienced in this east-southeast flow ranged from 75 to 90 mph officially, but unofficial reports came in at 95 or greater.
What I am showing you here is that the RGB Air Mass product may assist forecasters in the future with understanding where the highest risk for severe wind gusts may exist. The complication in this case came from having a hurricane with its associated wind field interact with a very strong, dynamic upper-level system that also transported high momentum air to the surface. These factors coupled with very low surface pressure (945.5 mb at landfall) most likely aggravated an already high impact storm surge event.
A special thank you goes out to John Knaff from CIRA for creating this product and to the NASA SPoRT team for making it available operationally at the NOAA Center for Weather and Climate Prediction.
I welcome feedback on this post. I will do my best to pull the wind data from ASCAT or OSCAT along with the stratospheric ozone retrievals from AIRS for a follow-up post in the next week. Thanks for reading!