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Tropical Storm Ophelia

#weather #phillyweather #philadelphia

I’ll be publishing this blog as a live blog. Check back as I add more entries.

Updated Fri 09/22 @ 10:32 PM — Tonight’s HRRR, RAP and the first 30 hours of the NAM. NAM-NEST and HIRESW models are in. The general trend is unchanged from my earlier 9:56 PM update.

The heaviest rains will be at the shore on Saturday, but significant heavy rain is forecast for the immediate Philadelphia area on Sunday. Totals for the two days remain a general 1.75-3″ in our area with 3-5+” possible as the shore.

Winds highest on Saturday. Here’s the latest NBM wind forecast for Blue Bell, PA—

Tonight’s 00z NBM wind meteogram for location Blue Bell, PA Mean Wind gusts 40 MPH. Standard deviation is dotted. (Click on image for a larger view.)

Update Fri 9/22 9:56 PM — The latest ECMWF and this afternoon’s NAM are forecasting the heaviest rain to occur on Sunday with the highest wind gusts Saturday afternoon and evening.

Updated Fri 09/22 @ 8:06 PM — The latest Canadian high resolution model (HRDPS) gives a very different forecast. This model only forecasts out 48 hours—

The latest (18z) HRDPS shows much heavier rainfall in our immediate area. The HRDPS was very good this past summer with thunderstorm predictions. I’m not sure that it will be as accurate with tropical or extra-tropical systems. (Click on image for a larger view.)

The HRDPS shows the highest winds about 9 PM Saturday evening.

Updated Fri 09/22 @ 7:54 PM — This afternoon’s GFS model has become available. It’s distribution of the heaviest rain is quite different than the earlier posted NBM model—

This afternoon’s (18z) GFS model shows most of the heaviest rain to the west of Philadelphia. Here’s the rain totals by Tuesday. (Click on image for a larger view.)

It should be noted that most models have reduced the peak wind gusts in our region to 35-40 mph on Saturday.

Previously Posted Fri 5:31 PM —

The model guidance was showing the development of this storm last weekend, which is impressive. At that time, I was saying that it looked like it would have “tropical characteristics” which meant that it had a warm core center.

Here’s the latest 12z NAEFS forecast for the current hour (4 PM Friday) showing the storm. The dull orange contour at its center is the 576 dm 500-1000 mb thickness line, indicating the storm’s warm core.

Today’s 12z NAEFS showing the Ophelia and its warm core center 9

Here’s the current water vapor image of the storm—

Water Vapor image at 4:30 PM with superimposed jet level windstreams and 500-1000mb thickness (RAP Model). Notice the 576 thickness center with upper winds shearing off to the west (blue). (Click on image for a larger view.)

Ophelia is expected to move into North Carolina and become non-tropical (“extra-tropical”) this evening upon landfall. Due to blocking high pressure to our north, the movement of this system will be slow and it will affect our region with rain and high wind gusts for much of this weekend.

Rain should begin here between 1AM and 3 AM Saturday morning and will continue on and off through at least Sunday.

The latest (12) ECMWF is not all that impressive with rainfall here —

ECMWF rainfall through Monday 2 AM. (Click on image for a larger view.)

The NBM rainfall for just for Saturday (from now through 2AM Sunday) is below—

This afternoon’s 18z NBM accumulated rainfall through 2 AM Sunday. (Click on image for a larger view.)


#Phillywx #Philadelphia #weather

Tropical Storm Ophelia

Updated Fri 09/22 @ 4:39 PM — When I updated this site this morning, the storm that is forecast to affect our weekend was still referred to as Atlantic tropical depression 16. It’s been named Ophelia My regular “Weekend Weather Forecast” will cover this storm and its impact on our area.

Look for a new post shortly.

Update Fri 9/22 8:38 AM — A quick update. No significant changes from last night’s forecast. Rain moves in from the southeast between 2AM and 4AM. Very windy with wind gusts 38-46 mph. Heavy rain on Saturday, especially Saturday late morning. Rain continues through much of Sunday. Total rainfall by Sunday evening 2-3.5”

Updates later today.

Update Thu 9/21 9:30 PM — The latest NAEFS ( a combination of our GEFS and the Canadian ensemble models) captures the current consensus guidance for this storm—

Today’s NAEFS model forecast for 2 PM Saturday shows the deep surface low almost vertically stacked under the upper level low.

By Sunday, 24 hours later, the surface low has filled and weakened and the upper level low lingers. It’s still raining here—

The NAEFS model at 2 PM Sunday. (Click on image for larger view.)

The latest NBM model just available show rainfall of 2-3” by Sunday evening and wind gusts of 35-45 mph.

Update Thu 9/21 5:03 PM — This will a difficult forecast to get right. The model guidance is all over the map…literally. Most models now have the strong tropical low pressure moving inland. Most, but not all, have this surface low pressure system rapidly “filling” as it encounters blocking high pressure, leaving a closed upper low. Most models have about 1.5-3” of rain through Sunday, with the majority of the rain Saturday. Heaviest activity closer to the shore is a safe, but not necessarily accurate emphasis.

It’s going to be difficult to pin down specifics regarding locations of the heaviest rains and higher winds. Stay tuned

Update Thu 9/21 8:29 AM — Last night’s ECMWF has finally joined our GFS model with a more coastal track and with the low pressure system becoming quasi-stationary as it moves over southern Delaware. The system will encounter high pressure to our north and will stall and somewhat “fill” (weaken).

ECMWF forecast 3 AM Sunday morning.

High winds and heavy rains still likely with this system.

Update Wed 9/20 9:52 PM — This afternoon’s ECMWF and NAEFS models, just available, have become a bit more similar, with the storm either moving a bit eastward, or slower just to our south. This trend would reduce the impact of the storm in our immediate area. Will have to see the trends with tonight’s models to get a better handle on this system.

Previously Posted Wed 9:02 PM —

As mentioned over past days, a disturbance off of the Atlantic coast of Florida will develop into an intense coastal low with some tropical characteristics. It’s expected to begin to affect our area during the predawn hours of Saturday morning.

The majority of models have this system moving up the coastline, with the exception of the ECMWF, which continues to have the system bend away from the mid Atlantic coast. (Tonight’s GEFS does have the storm blocked from northward movement as it approaches the Delaware coast with a slight turn eastward. This somewhat supports the ECMWF track, but it’s too soon to hang our hats on this forecast.)

Heavy rain, high winds are likely on Saturday if it follows the track of the GFS, Canadian and German ICON models. Rainfall totals of 1.5 to 3 inches are likely, with wind gusts 35-50 mph. Impacts will be significantly less if it follows the ECMWF track.

Here’s the latest Canadian RGEM

18z Canadian RGEM forecast total rainfall for 2AM Sunday. (Click on image for larger view.)

So, this could be a major storm for our area or it might move eastward enough to significantly reduce its impact. Stay tuned.


#Phillywx #Philadelphia #weather

This Weekend’s Storm

Updated Wed 09/20 @ 8:37 AM — The models are in good agreement (with the exception of the ECMWF) that a major Nor’easter with some tropical characteristics will affect our area beginning Friday night.

The latest GFS shows this storm at 2PM Saturday—

06z GFS shows major low pressure system moving up the coast at 2 PM Saturday. (Click on image for a larger view.)

Anywhere from 1.5-4 inches of rain are possible with this system along with high winds and coastal effects.

The latest German ICON model shows very high rainfall possible—

Latest ICON model shows large areas of 3-4 inches of rain by Sunday afternoon. (This model is at the upper end of the rainfall forecast range.)

Wednesday Through Sunday Outlook

Update Tue 9/19 9:28 PM — Continued fair weather through early Friday. Increasing cloudiness expected during the day on Friday.

The models have come together forecasting a slow moving coastal storm, held back by a westward closed upper low. This is expected to move in Friday night.

NAEFS forecast for 8 AM Saturday. ( Click on image for larger view.)

The ECMWF, which had been holding back on the development of this system, has joined the other models forecasting this storm. It is a bit slower than the GFS and NAEFS, with the rain moving in during the day Saturday. Currently, it looks like it will be raining most of Saturday with somewhat light showers on Sunday.

Sometimes these storms move out faster than the model forecasts, so there’s some hope for Sunday.

Tuesday – Friday Outlook Update

Updated Mon 09/18 @ 6:23 PM —The low pressure system off of the coast will move northeast and high pressure builds in for Tuesday through Thursday.

Fair skies and seasonably mild temperatures expected.

ECMWF Temperatures forecast through Friday (Blue Bell, PA) (Click on image for a larger view.)

Clouds move in sometime on Friday.

There’s uncertainty with the low pressure development off the Florida coast. The NAEFS (combined GEFS and Canadian Global Ensemble) continues to forecast an “inverted coastal trough” moving in Friday into Saturday with clouds and an increasing chance of showers. The ECMWF is NOT currently on-board with this system moving northward. I’m leaning towards the NAEFS—

NAEFS forecast for Friday. Inverted trough along the Atlantic coastline of Florida is forecast to move northward toward us. (Click on image for a larger view.)

Update Sun 9/17 11:09 PM — Tonight’s models are forecasting a slower exit of the showers Monday. We may still see some showers in Philadelphia and eastward as late as 1-2 PM.

Previously Posted Sun 8:03 PM —

A weak coastal low will move northeast Monday. Showers may linger until 10 -11 AM and clouds will linger into the early to mid afternoon.

High pressure builds in for Tuesday through much of Friday—

NAEFS forecast for Wednesday at 11 AM. High pressure over the Mid Atlantic and Northeast will keep sunny skies and and seasonable temperatures. (Click on image for a larger view.)

Average seasonal high temperatures this week are 75º-76º. Temperatures this week will be close to slightly above seasonal averages.

So an uneventful weather week is in store for us.

Of interest is a potential tropical or semi-tropical system expected to develop off the Atlantic coast of Florida sometime on Friday. This is forecast to move north and bring clouds and rain late Friday into Saturday. Things will likely change by the time Friday rolls around.

Weather… and Other Things 'Up in the Air'