Tropical Storm Isaias Forms, Threatening Mid-Atlantic Rain by Sunday

Q: How could the unpredictable path of Tropical Storm Isaias turn a sunny Baltimore weekend into a sudden flood risk?

A sunny Baltimore weekend could quickly turn into a flood threat if Isaias tracks far enough north and east to funnel deep tropical moisture into the Mid-Atlantic and slow down over the region. That is the main uncertainty forecasters are watching. Current forecasts keep Baltimore warm and mostly dry through Saturday, but Isaias is expected to move inland from the Gulf and drag a plume of very humid tropical air northward. If the storm’s path lines up with Maryland, that moisture could be squeezed into bands of heavy rain late Sunday into Monday. Tropical systems can produce rainfall rates high enough to overwhelm storm drains, small streams and low-lying roads in a short time. The risk depends less on whether Baltimore sees rain at all and more on the storm’s exact track, speed and strength. A farther-west path could keep the heaviest rain away. A track closer to or just west of the Appalachians could place Baltimore on the wetter eastern side of the system, where tropical rain bands are often most intense. If Isaias slows or interacts with a front, rainfall could repeat over the same areas, sharply increasing flash-flood potential. Forecast guidance tied to the storm has already highlighted 3 to 6 inches of rain in broader impact zones, with isolated totals up to 10 inches near heavier bands. Baltimore is not in that core forecast now, but even lower totals can cause urban flooding if they fall quickly. That is why forecasters stress monitoring updates through the weekend.

3 articles · Updated · Fox Baltimore · Oct 7

Tropical Storm Isaias formed and could drive rain chances sharply higher in the Mid-Atlantic by Sunday and Monday.
A Gulf landfall as a hurricane is possible by Friday before the system races north inland through the Mississippi Valley and Deep South, pulling tropical moisture toward the region.
Baltimore is expected to stay dry through Saturday, with highs warming from the low 70s Wednesday to the upper 70s Thursday before settling back into the 70s Friday and Saturday.
The forecast focus shifts this weekend from a brief warm, quiet stretch to Isaias’s track and timing, which will determine how much tropical rain reaches the Mid-Atlantic.