Monthly Archives: August 2019

Philadelphia Area Weather Forecasts

LABOR DAY WEEKEND FORECAST

High pressure that brought the delightful weather on Friday will remain with us one more day.  It will slowly move off to the northeast over the weekend, giving us an easterly wind flow by Sunday.

A low pressure system in the Midwest will be blocked by this high pressure (the same high blocking the northern movement of Hurricane Dorian), but some upper air disturbances will attempt to invade the retreating high pressure from the west on Sunday and Monday.

Saturday will be mostly sunny, with some occasional fair weather cloudiness.  High will be near 80.

Some of the moisture and energy from the Midwest system will move in on Sunday.

On Sunday:  Combined with a surface easterly wind flow, there will be considerable cloudiness on Sunday, perhaps with occasional sun, although I’m thinking full cloudiness is most likely.  There is the chance that some widely scattered showers may develop, although most of the models keep us dry during the day, despite some disturbances moving through.  High 79.

On Monday, the trend on Sunday continues with mostly cloudy skies and a higher chance of widely scattered showers.  High 80.

As mentioned yesterday, Dorian may indirectly influence our weather this weekend with increased high level moisture from the storms outflows.

Speaking of Hurricane Dorian, a review of the latest model errors suggests that the newly developed Navy COAMPS-TS model is doing well with this storm.  Interestingly, it was one of the first to show a trend of stalling off the Florida coastline and moving northward.  The most recent GFS has begun to suggest the same general movement.  The National Hurricane Center still has the storm hitting Florida, somewhat north of Palm Beach, on Tuesday.

Here is the latest Navy COAMPS-TS model prediction for track and strength of the storm—

US Navy COAMPS-TS model forecast for Dorian

Notice that it predicted the strengthening to a category 3 today, but it is predicting a subsequent weakening, then strengthening again before a delivering glancing blow off the central the Florida coast.

Philadelphia Weather Outlook

LABOR DAY WEEKEND WEATHER OUTLOOK

Hurricane Dorian is currently forecast to approach the eastern Florida coastline sometime Monday.  The  hurricane-specific models and their variants (and there are many of them)  have quite a spread  with the prediction of landfall locations but landfall somewhere around Cape Canaveral, Florida is currently forecast on Monday.

The model error-tracking done at the NCAR  (National Center for Atmospheric Research) in Colorado shows all models to have current errors in predicting the position of this storm of at least 50-60 miles over the past 24 hours. Errors in predicting the location of Dorian over the past 48 hours have been over a 100 miles off.   So accuracy is not there yet with this storm track, regardless of model.

The reason I bring up Hurricane Dorian is not because it will directly affect us over the weekend. But there will be indirect effects.

My experience with weather over many years has led me to notice that a strong tropical system in the western Atlantic seems to bring havoc to model forecast accuracy here.  I don’t know why that happens but there’s some effect. 

As a result, confidence in the model weekend forecast is somewhat lower than usual.

Already, a weekend that had been looking quite beautiful just a few days ago is now looking to have significant high, thin cloudiness, especially on Sunday and Monday.

Saturday appears to be the nicest day, especially from Philadelphia south and east.

Some scattered showers are possible on Sunday.   The humidity might be higher than currently forecast.

I’ll take a better stab at the forecast on Friday.   Expect changes in the forecast this weekend.