As of 320 pm EDT Hurricane Sandy was located around 17.9N 76.7W and is currently lashing Jamaica with hurricane conditions. Max sustained winds were 80mph with a centralized pressure of 973mb. Sandy is moving towards the north at around 12 kts due to cross-equatorial forcing from the monsoonal trough below and a trough located across the central Atlantic. This trough is helping to cause upper level shear of 60-70kts to the northeast of Sandy helping to ventilate her outflow.
This water vapor imagery/Upper-Level wind overlay courtesy of CIMSS shows these features quite nicely
This trough is being deepened by a combination of the anticyclonic flow from the mid level high pressure system located over the eastern United States, outflow from Sandy and a jet max associated with a mid to upper level low pressure system near Nova Scotia. This graphic courtesy of NCAR shows these features well. This was from 12Z this morning ran out 12 hours to 00Z which is close to current time.
You can see a jet max near California/Nevada helping to dig a trough across the central United States. You can also see a low pressure system in southern Canada that may very well be a player later in the forecast. You can also see the low near Nova Scotia with the associated jet max helping to dig this feature further.
An anticyclone has formed over the center of Sandy although displaced slightly to the south which has brought upper level wind shear down to near 5-10 kts over her. The band of high shear to the north should move slowly to the east and should not affect her much near the Bahamas. As the mid- level high pressure system moves eastward upper level winds should be in the 10-20 kt range over her in the next 48 hours.
These two graphis show the high pressure over the eastern United States quite well. Forcing from the trough digging into the central United States will eventually push this high further eastward. This high will then get squeezed between the central U.S. trough and the developing low pressure system over the northern Atlantic. That coupled with the southern flank being eroded by Sandy should weaken this high over the next 24 to 36 hours.
This graphic is from the 12Z GFS and shows 850 mb winds 36 hours out. You can see Sandy making her close approach to Florida while the high moves northward and slowly begins to erode. This pattern could trap Sandy in a period of weak steering currents and could move erratically during this period. This low pressure system that will be moving into southeastern Canada should amplify enough as to lift Sandy northeastwards when a secondary trough should be able to lift her almost out to sea. Some of the models especially the Euro and the GFS show this trough becoming very strong. This trough then turns Sandy in a funky type loop back to the northwest towards New England. This would be a very interesting scenario and one that will have to be looked at closely. Right now I am leaning on the fact that the trough should move progressively taking Sandy out to sea with it. Based off of the forecast above I would not be surprised to see Sandy peak in the Bahamas at or near 90-95 mph. I am expecting 50-60 mph winds for SE florida and some higher waves being produced for the eastern seaboard. This forecast could change with future model runs.