The blocking pattern that has given us the extended mild and dry pattern will weaken a bit but continue to block the progress of a frontal boundary and will likely also block the northeast movement of tropical storm Joaquin.

Heavy rain for tonight (Tues) will  likely be more focused west and north of Philadelphia, but we will still receive some moderate to heavy rain, tapering Wednesday afternoon.

The front stalls to our south  and areas of low pressure move along the front, bringing more rain Thursday into Friday.

Tropical storm Joaquin may strengthen to hurricane status before moving into the Carolinas or even Delaware sometime between Friday and Sunday.    This situation needs to be watched, since heavy rain and high winds are possible.

There continues to be major differences between the GFS and NAM models’ handling of the coastal low pressure system expected to move up the coast, with the NAM shunting the precipitation to out west until late Sunday, with the GFS bringing the rain up into PHL during the afternoon.

I’m still leaning towards the drier  NAM. But this will be a good test of the two models for this season.  Updates later.

1pm update:  the GFS model is looking more like the NAM model -Keeps the showers to the south and west on Sunday, slight chance of light showers about noon.  Still a lower confidence forecast.

9pm update:  models keep it dry in Philadelphia until late afternoon or early evening Sunday.  But it will be a close call with a sharp precip cutoff.  A model error could kill this forecast.

Saturday will be partly sunny and windy. High 72.

Sunday will be cloudy and windy with showers possible late afternoon or evening.