N90 TRACON Controller reported the adjacent PHL TRACON vectored an aircraft deviating for weather into their airspace without coordination and on a conflicting heading with other aircraft deviating for weather.

Narrative

A lot of thunderstorms were in the area. LGA Departure was vectoring aircraft in between two weather cells around TEB airport at 10;000. This was the only gap through the weather in LGA airspace. PHL Area C decided to vector aircraft through the same break in weather cells at the same altitudes in LGA Departure airspace without any communication. When LGA Departure noticed the opposite direction aircraft at the same altitude; they descended their aircraft to 9;000 to get underneath. Unfortunately; since there was no communication with PHL Area C; PHL decided to take the same action and descended their aircraft to 9;000. The fact that there was no catastrophic mid air collision is nothing short of luck; as these aircraft were converging at high speeds at the same altitude in between dangerous thunderstorms off their left and right sides. The EWR Area has been relocated from N90 to PHL. As a result the air traffic operation is inherently less safe. It takes longer now to communicate in safety critical situations than it did prior to the airspace relocation. The lack of internal coordination; which was lost when EWR Area relocated to PHL; is the reason why this was so incredibly dangerous. This could have been easily mitigated by these controllers speaking to one another in the same room. I recommend the EWR Area be relocated back to N90 from PHL. It is the only way to fix the many safety hazards that are attributed to splitting apart this air traffic operation.