Re: MJO and Atlantic Basin / Weak Systems
Posted by
Jake on 8/9/2012, 11:20 am
Hanna, I don't think there's a connection. We've had many years of active MJO Phases in the basin and have resulted in above average years storm wise, however US landfalls were low.
Although a positive or active phase will increase cyclone formation, ultimately, the steering pattern and genesis location are the main landfall factors.
MJO analysis have should to increase mixing ratios in 850-500mb vorticity max, as strong mixing during the upward pulse help trigger meso-scale convection in the genesis region. Lastly, the NAO while in a negative phase have also shown to increase cyclone formation. NAO is forecast to be slightly below normal through Aug 16th.
See below good read!!!
Kocher 2000). Changes in the NAO are thought to affect the tracks of
tropical cyclones in the North Atlantic (Elsner et al. 2000b). For example, when the NAO
is positive (negative), the Atlantic subtropical high shifts eastward (westward) and gains
strength (weakens), steering tropical cyclones along the eastern seaboard (into the Gulf of
Mexico). The strength of this association over time will be examined in this research.
The NAO Index (NAOI) is a normalized pressure difference between Iceland and
the Azores. When the NAOI values are positive, the subtropical high pressure over the
North Atlantic is stronger and located more to the east in the Atlantic. This allows for
more recurving storms, potentially indicating a greater risk for storms to make landfall in
the northeast U.S. In contrast, a negative NAOI results in a subtropical high pressure
situated more to the south and west, and relatively weaker than the positive NAOI
counterpart. This situation results in tropical cyclones being steered more to the south,
and often results in tropical cyclones threatening landfall along the coastline south of
35°N (Elsner 2001, in review). Analysis of the state of the North Atlantic Oscillation
(NAO) indicates that the Gulf coast of the U.S. is more susceptible to major hurricane
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landfalls during a relaxed phase of the NAO, whereas the East coast of the U.S. is more
susceptible to a major hurricane landfall during an exited phase of the NAO (Elsner et al.ation. |
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