Tropical Storm Melissa was nearly stationary in the central Caribbean early Friday, with forecasters warning it could soon strengthen and brush past Jamaica as a powerful hurricane while unleashing catastrophic flash flooding and landslides in southern Haiti.

The two categories combined make up about 17 percent of all hurricanes in recorded history. Those reaching Category 5 — like Melissa — historically make up more like 4 percent of hurricanes. And fewer than half of the strongest two categories of hurricanes go on to hit land at such intensity.