From MTA:

“The next phase of the Hudson Line station rehabilitation project will begin on Monday, January 14, 2008, and will last for approximately 18 months. During this phase, we will replace the inbound platforms at Philipse Manor, Scarborough, and Ossining stations.

This work will require that we continue to change the way in which we operate trains from Morris Heights to Ossining during the AM Peak. Therefore, customers will still board their morning trains from the opposite platform. (In other words, northbound trains will be arriving on southbound platforms, and southbound trains will be arriving on the northbound platforms.)

Additionally, weekday off-peak customers at Tarrytown, Philipse Manor, Scarborough, and Ossining stations will generally use the northbound platform for ALL trains (southbound and northbound) during this project phase.

Please look for signage with exact details at your station, and also listen for announcements in the event that operating conditions require a last-minute revision to track assignments.

We thank you for your patience and understanding.”