Previous seasons dominated by low vertical instability?

[weatherwindow]

Over the course of 25 years, I believe this is the first year in which "lack of vertical instability" has been noted as having a major impact on the hurricane season . A question for the board: Have previous seasons been noted as being adversely affected by lack of instability? What is the likely cause of a season-long lack of vertical instability?

[weatherwindow]

can any of the promets answer these questions?......my thanks in advance.....rich

[wxman57]

The archive of instability data only goes back to 2000, but none of the years from 2000 through 2010 comes even close to the low instability in 2011:
http://rammb.cira.colostate.edu/project ... /archived/

[CrazyC83]

1990 perhaps? Didn't that have a lot of storms that were mostly weak?

[wxman57]

1990 perhaps? Didn't that have a lot of storms that were mostly weak?

As I said, I don't have the data prior to 2000.

[weatherwindow]

The archive of instability data only goes back to 2000, but none of the years from 2000 through 2010 comes even close to the low instability in 2011:
http://rammb.cira.colostate.edu/project ... /archived/

looking over the data for the subbasins...i thought it was interesting that the instability remained at or above average for all basins until july and then the instability took a nosedive simultaneously across all basins thru the peak of the season aug-sept-oct....any thoughts as to why it would fall simultaneously in all sub- basins?

[Ptarmigan]

From August to September

1990
Air Temperature Anomaly 700 mb


Specific Humidity Anomaly 700 mb


The air temperature at 700 mb level or 10,000 feet is normal to cooler than normal for the most part, but not unusually cold. The air is drier than normal at 10,000 feet especially over the Caribbean and Gulf of Mexico.

Active Season (1995, 2005, and 2010)
Air Temperature Anomaly 700 mb


Specific Humidity Anomaly 700 mb


The air temperature and specific humidity is higher than normal over most of the basin. It is not abnormally warm at 10,000 feet. The level of humidity is abnormally high at 700 mb, which makes it more conducive for tropical development.

2011
Air Temperature Anomaly 700 mb


Specific Humidity Anomaly 700 mb


The air temperature in 2011 is warm at 10,000 feet, but again not unusually warm. However, the specific humidity is higher than normal in the Atlantic and parts of the Caribbean. Those areas saw most of the development. However, Gulf of Mexico is drier, which is no surprise from the ongoing drought. Gulf of Mexico has been hostile in 2011.