NYCEM has placed New York City under a Travel Advisory for this afternoon and evening as the risk for excessive rainfall has increased from Slight to Moderate, Level 3 of 4.   There is an increased risk of flash flooding, and conditions could become dangerous with little warning. The heaviest rain may not hit every neighborhood, but where strong storms develop, streets, low-lying areas, subway entrances, and basement spaces could flood quickly.   Prepare now. Plan for possible travel delays and disruptions. Allow extra time, check weather and transit conditions before leaving, and be prepared to delay or change your plans.   If you live in a basement apartment or other below-grade space, be ready to move to a higher floor or safer location before flooding begins. Never walk, bike, or drive through floodwater.