Sunday, August 28, 2011

August 28, 2011 After The Storm: Analysis of Wind and Rain

Surface Analysis, 8 AM EDT:   The storm's peak winds and rain were exiting Baltimore at this time.   The heavy rain shield remained highly asymmetric, concentrated west and north of is typical for tropical systems undergoing extratropical transition.  Dry air off the U.S. mainland was being swept into the southern half of Irene, evaporating rain and clouds there.  The stationary front - initially over the Appalachians - began merging with the large wind circulation.
Regional Scale Surface Analysis:  This short movie loop shows the extremely large footprint of the pressure field, and intense pressure gradient.   The radar is superimposed on the pressure field, so you can watch both features co-evolve.   The loop shows hourly fields from 10 pm EDT on 27 August through 6 AM 28 August.
Rain Accumulation:  Here are two scales of charts:  Regional scale and local scale.  Both maps are derived from radar estimates.   These totals have yet to be compared with gauge estimates.   Extreme point estimates may not be accurately measured by radar.  But in general, the rain accumulation agrees quite well with the predictions for our region.
Winds:  Shown here are several time series analyses of hourly winds.   The graph below shows the sustained winds, in mph, at three stations:  Dulles (IAD), Baltimore (BWI) and Washington Reagan (DCA).   DCA was the winner with highest sustained wind, which peaked above 40 mph at 1 AM.  I constructed these graphs very quickly...the number "1" across the bottom starts the graph at 9 AM on August 27.  The observations are hourly and end at 11 AM this morning.
Here are similar plots but comparing sustained wind vs. peak gust (mph) at each of the three airports.  The time convention is the same as described above.  At BWI, the peak gust was 51 mph at midnight.  In the BWI plot, you can see evidence of higher gusts when multiple rain bands moved through.  The highest gust was at DCA - 57 mph at 1 AM.
Wind Damage:  Here are utility outage maps I grabbed off the web at 9 AM this morning.  Outages were most extensive along and east of I-95...closer to Irene's center of circulation.



  1. 5.25 inches at my house in Columbia

  2. My Davis tipping bucket says 3.86" since tippers notoriously under report my guess is closer to 4.25-4.5" which make sense. Near St. Agnes.