The focus period for the long term forecast will be Wednesday night
through Thursday night (at least). This 24-36 hour period has the
potential to deliver another round of 2-3 inches of rain to the
region which (I`m sure we don`t need to remind you) only recently
received this much rain and continues to see some rivers in flood
stage. The most important thing to determining where/if we deal with
exacerbated flooding will be the ultimate track of the storm and the
axis of heaviest rainfall. It is too soon to have a high degree of
confidence on where this axis sets up, but the most recent ECMWF
global guidance has come west, in line with the GFS/Canadian
guidance showing those large rainfall amounts over interior southern
New England rather than further east/offshore. Of course, we don`t
want to focus on deterministic model runs, but that agreement isn`t
what you would want to see if you`re hoping for a miss offshore. At
this time frame we focus on ensembles, two of which (the GEFS and
EPS) are indicating a 20-40% and 10-30% chance of AOA 2 inches of
rain respectively. Not huge numbers, but 3 days out certainly
indicative of potential for concern given how saturated the
ground is already. The atmospheric moisture and dynamics are
there, with a 1.25" PWAT plume directly from the Gulf of Mexico
and large scale ascent from favorable placement beneath a 150 kt
upper jet, but just how/if the northern and southern streams
interact is unknown at this time. Additionally, probabilistic
hydrographs from the NAEFS and GEFS indicate renewed flooding
for RI rivers. This system will also bring a period of gusty
winds as it passes late week.
