Continuing Our Summery Ways But Driving Cristobal Away
It's been four days straight of 90+ in Philadelphia and the heat goes on tomorrow with yet another day of sizzling heat and humidity. Philadelphia's 95 degree high was not as high as Friday's 96, but when combined with dewpoints in the low 60's the heat index value topped out at around 95 for much of the region today. While hot, we have been avoiding heat warning criteria (heat index values at or above 100) as dewpoints continue to drop during the day due to atmospheric mixing thanks to lots of sunshine.The wind flow at the surface on Sunday will be from the south to south-southwest, which is a more humid wind direction than the downslope-like southwest is since the wind flow comes off of the Atlantic. Temperatures will be hot again, with high temperatures likely in the 92-95 degree range across the Philadelphia and I-95 corridor but with higher dewpoints (closer to 70) we should see heat index values near 100 tomorrow. As a result the excessive heat warning will continue for one more day. As of now, I think Sunday is the last day of 90+ heat as I do think we'll see more clouds and showers on Monday in the region so temperatures will still be plenty warm (upper 80's) but not quite at the magic 90.
Scattered thunderstorms are more likely to fire up tomorrow afternoon and evening, mainly north of the PA Turnpike and I-195. These storms will have a bit more movement and a bit more coverage to them than storms of the last couple of days as they are associated with a frontal boundary that lies across New York and New England. This boundary will slide slowly to the south and east over the next two days, eventually setting up shop off the coast.
What this boundary will do is keep Tropical Storm Cristobal to the east of us and keep the significant wind and heaviest of rains out to sea. However, the circulation of Cristobal could help draw additional tropical moisture into our region so there could be more heavy showers and storms on Monday for much of the region and on Tuesday along the coastline than what model guidance is currently suggesting. This is something we'll have to watch as the front drops south and Cristobal continues to churn up the coast. It is expected to strengthen to a strong tropical storm and has an outside chance of becoming a minimal hurricane before encountering cooler waters and the frontal boundary in a couple of days (a good ways to our east).
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