The Front Right Quadrant

  Any tropical cyclone is dangerous and should never be taken lightly, but often there is one region of the storm than is especially intense: the front right quadrant (in the northern hemisphere). The location of this zone is determined by the direction the storm is moving. This is the place where the counter clockwise rotation of the wind is oriented in the same direction as the storm's motion. The result is a region where the maximum wind and storm surge will likely occur.
  In the case of Hurricane Isaac, which made landfall last night (August 28), the front right quadrant was essentially the northern quadrant of the storm, which was moving to the northwest. Unfortunately, Isaac made landfall just to the west of the Mississippi River, so the winds and the surge pushed against the river's current. For a river as large as the Mississippi, this can easily result in flooding. Upstream lies New Orleans, where the river makes a sharp turn, right near downtown. To compound the issue, Lake Borgne (which really more of a bay), lies immediately to the east of the city and is oriented roughly east-west. As Isaac tracked to the south, southwest, and west, the lake acted as a funnel, piling the storm surge along its west coast, right towards New Orleans. In fact, NOAA's SLOSH storm surge computer model predicted the highest surge in the entire Gulf to be in the west end of the Lake.
   As the storm slowly makes its way inland, the forecast track takes Isaac (or its remnants) along, and roughly parallel to the Mississippi River, then along the Ohio River. Both of these rivers have large watersheds and the storm's front right quadrant will remain over these watersheds the whole forecast period (five days). Below is an image of the storm's predicted path (in white) along with its error bounds (in grey). The bright green contours highlight regions where the predicted rainfall total over the next five days is forecasted to exceed three inches and the blue contours show where over seven inches of rain are predicted.
   The second image is an animation ending September 2 at 00Z that simulates what a weather radar would see. The computer model this comes from did not predict the most accurate track for the storm so far, but the general distribution of rain should be close enough to illustrate the point. The bumps in the display are present because the displayed data has been "draped" over a three-dimensional topographic map (which is invisible otherwise), this helps show what direction the rain will likely run once it reaches the ground. Finally, the cyan colored lines are major rivers and lakes, with the mouth of the Mississippi River in the foreground and the southern end of Lake Michigan along the back side of the image.



5-day predicted rainfall totals and the predicted track of Isaac
 

simulated radar animation of rainfall