Limitations of the Meteorologist

Over recent years, the National Hurricane Center in Miami has increased forecast accuracy for storms.  The error in storm tracks has reduced by hundreds of miles, meaning less money is spent on evacuations due to fewer false alarms.  Short term intensity, however, has continued to be a problem.  This leads to the Central Pacific Hurricane Center (CPHC) in Hawaii, who like the NHC is a subset of the National Weather Service.

Yesterday, Tropical Storm Genevieve was being forecast to move west, then take a slow turn to the north.  Along the way, the storm was to strengthen to strong category 1 winds (74-95 mph).  The track forecast has been quite accurate.  Error has been kept within the CPHC/NHC guidelines.  The intensity forecast, on the other hand...

 Genevieve is now forecast to be a category 5 hurricane (winds > 135 mph).  This left me wondering where the forecast went wrong, and if there actually was a chance of the forecast being correct.

The models from yesterday show a consensus on the storm eventually reaching category 3 or 4 strength over a 24-48 hour period.

The Coupled Hurricane Intensity Prediction System (CHIPS) models had a similar agreement, except for CHP6.  CHP6 actually predicted this accelerated strengthening.  CHIPS is just a two dimensional model that uses radius and height as its coordinates.  To counter this, CHIPS uses vertical data from the Global Forecast System (GFS) model to create a full-storm profile.  Through this, CHIPS can simulate the effects of wind shear on storm intensity.  CHP6 represents the upper boundary of the storm intensity forecast by increasing the storm intensity and setting vertical wind shear to 0.  The problem here is that CHIPS is one of many experimental model systems and is not part of the official forecasting system yet.

 

 So I decided to conduct my own analysis of this using the GFS model.  Using this model proved valuable as the animation below shows.  The red wind barbs show 200-mb winds, and the magenta barbs show 850-mb winds.  As can be seen in the animation, there is not much of a difference between the two in strength.  There is some directional shear, but this kind of variability is normal and does not affect the storm intensity.So Tropical Storm Genevieve was actually entering the low speed shear environment favored by CHP6.  However, CHP6 does not use the GFS 3-D or any of the same environmental parameters (carbon dioxide, ozone, etc.).

 

The Central Pacific Hurricane Center got caught by a strange set of circumstances.  Few storms form in the Central Pacific each year, with some years even having zero storms.  Overall, anomalous occurrences such as this should not be judged harshly as there are dozens of model outputs for the forecaster to analyze.  Few storms of this strength enter this region, so events like this are  opportunities for meteorologists of all backgrounds to learn.  The developer of CHIPS, Professor Kerry Emanuel of Massachusetts Institute of Technology, should be quite proud of his work this morning.