Kingarabian wrote:Eric Webb wrote:Kingarabian wrote:
Agreed that much of the favorable rising air moving into the Atlantic will not do much. Even if forcing lays off for a while in the Pacifc, June in the EPAC has gone bonkers. +PMM and warming ENSO regions will only induce more local development, meaning lower pressures will be predominantly over the EPAC and higher pressures will likely be situated over the Caribbean and MDR.
If (big IF** (some of the intraseasonal forcing may be washed out in the model)) the EPS is right, just wait til you see what July has in store for the EP, certainly won't be long before we get those classic, very long-lived and long-tracked TCs in the EP that attempt to threaten Hawaii. If the globe continues to warm, there will eventually come a day in the extremely distant future where the mean climate will be conducive enough by itself to legitimately threaten Hawaii w/ tropical cyclones every year even without any help from an El Nino or a +PMM as is the case now.
What has protected Hawaii a lot and helped the negate the threat of rising SST's temperatures around Hawaii, is shear. I know that El Nino reduces shear in the CPAC/EPAC, but what about a +PMM? Is it similar to the Atlantic, in where the SST configuration/temperatures also influence shear patterns?
The PMM is an analogous mode of variability to the Atlantic in that they both involve interactions between mid-latitude rossby waves breaking into the tropics which affect the trade winds and the meridional juxtaposition of their respective intertropical convergence zones (ITCZs) towards the warmer hemispheres. Many including Markami et al (2016):
https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-16-0424.1 actually show through NWP simulations which are able to separate the influence of the ENSO and PMM that the PMM actually plays a larger role in Eastern Pacific TC seasonal activity than ENSO, although it plays a significant role west of 120W.
The positive phase of the PMM decreases the climatological shear over the EP, raises the ITCZ further from the equator, making it more unstable and prone to vorticity roll-up due to greater coriolis defletion. A +PMM also increases the geographical expanse of the EP's main development region by warming the SSTs to the NE near the edge of the basin where the cool California current demarcates the poleward extent of TCG and ACE accrual in the NE Pac. In addition the +PMM is also often coupled to ENSO and both contribute to cyclonic vorticity advection in the NE Pacific by reducing the climatological trade winds.
