Harlem River Closure, Thu, Sep 8, 0455-0505, from 3rd Ave Bridge to RFK/Triborough Bridge

Just a heads-up. This appears to be very early in the morning but in case anyone planned to be out on the Harlem Thursday morning see below.
This is the entire notice from Homeport.  No explanation was provided.:

Re: Harlem River Closure, Thu, Sep 8, 0455-0505, from 3rd Ave Bridge to RFK/Triborough Bridge

REQUIRED SAFETY MEASURES:
1.    The Harlem River will be closed on Thursday, September 8th, 2011 from 0455-0505. No vessels will be authorized between the Third Ave Bridge and the Triborough/RFK Bridge.
2.    NYPD and FDNY Harbor vessels will be on scene.
3.    Miller's Launch will have a small boat near each bridge to also notify mariners of the closure.
4.    POC: LT William George at (718)-354-4114.