Wednesday, October 24, 2012

Morning Update On Sandy

Sandy continues to intensify this morning in the Caribbean, moving northward towards Jamaica and Cuba, both of which it will cross over during the next 24 hours.   As of 5 AM, Sandy has 70 mph max winds and will probably reach hurricane status later this morning or this afternoon.  Modeling still varies a fair amount between the GFS, Euro, and Canadian regarding the final track and impact with the storm.  However, the GFS did shift left from last night's's a bit closer to the coast with the track but still a lot further east of the coast than the Euro.

The Euro track shifted left a touch from last night, bending the storm back for a "landfall" to the north of Atlantic City.  I posted a wind graphic below to show how the storm's landfall spot along the Central Jersey coast in the Euro scenario for early Tuesday morning.  While Sandy is very likely not to be tropical in any "coastal bomb" scenario by the time it reaches our latitude, landfall points do matter somewhat.

While a nontropical storm has its strongest winds away from the center, the trajectory of winds do matter in terms of coastal flooding and wind strength.  Let's assume for a moment that the coastal scenario plays out and it follows the Euro scenario depicted above.  In such a scenario, winds will be from the east to the north of the center of the low, pushing water onshore and increasing tidal flooding to the north (or northeast) of the low's center.  Those locations to the south of the low get lots of wind but with an offshore flow the issue would be along the lines of flooding from the back bays as winds would push water to the barrier islands.  In some respects, wind strength may be a bit stronger north of the storm center than south -- not much, but an onshore wind is going to have less frictional forces (no trees, houses in its path) and can pick up a bit extra momentum.  In this case, wind gusts could be 50-60 mph south of the low, 60-70 mph north of it along the coast.  That's not a forecast -- it's what the model scenario, played out as the Euro predicts, could produce.  Still plenty bad but it's an example of how storm track does matter since the strongest wind gusts could ultimately be to the right of the track of the storm.

Inland, a closer brush with the low track throws additional rain back towards us.  Any of the last umpteen model runs of the Euro show a few to several inches of rain across Pennsylvania and New Jersey.  Something akin to the Canadian or a "middle ground" scenario would bring markedly less rain to the city but would likely hit New England pretty hard.  We would mostly deal with wind here.

The ensemble modeling average with Sandy (including the GFS ensemble) still shows a close to coast track, pretty similar to what was detailed yesterday.  More of the individual GFS ensembles continue to show a bend back scenario a la what the Euro is depicting although they vary quite a bit in terms of where the bend back takes place.  The white track on the graphic below is the operational, which still shows the storm farther out to sea.

Getting caught up in further specifics with a paper modeled storm that's six days away may be an exercise in futility if the GFS operational ends up being right but the majority of computer modeling out there continues to show the possibility of Sandy becoming a coastal bomb early next week.  Track and details are definitely far from certain with the storm system...and as outlined above, track *does* matter for those on the coast in terms of wind and water trajectory and for us inland folk, if the Euro were to verify, we'd get a lot of rain early next week.