Monthly Archives: September 2023

Tropical Storm Outlooks

Tropical Storm Ophelia

#weather #philadelphia #phillyweather

Sunday Forecast Update

Updated Sun 09/24 @ 5:20 PM — The main area of rain is exiting our area, but continued light drizzle and showers are still forecast through the night.

Radar at 4:48 PM Sunday with superimposed RAP model jet level windstreams (orange) and moisture convergence (blue)

The NBM has the [heavy] rain exiting in time for the Phillies game at 6 PM—

Today’s 18z NBM simulated radar (colorized contours) and cloud ceiling at 6 PM. (Click on image for a larger view.)
Sunday Forecast Update

Updated Sun 09/24 @ 11:40 AM — Rain will continue through this afternoon and tonight. There may be some periods where the rain lets up, but expect it to return.

It looks like the mastodon wxcloud.social server is offline

Current water vapor image with superimposed RAP model parameters shows an area of vorticity and instability approaching. Showers and even some thunderstorm activity is possible this afternoon —

Current WV and RAP potential vorticity and MUCAPE (Click on image for a larger view.)

The latest HREF model shows considerable additional rainfall for our area for the next 24 hours—

This morning’s 12z HREF forecast for additional accumulated rainfall 8AM Sunday through 8 AM Monday. (Click on image for a larger view.)

Latest MRMS (10AM) total estimated rainfall over this weekend so far—

Sunday Forecast Update

Updated Sat 09/23 @ 9:46 PM — This afternoon’s and this evening’s early models have periods of rain continuing through the night and much of Sunday into Monday morning!

There may be a break in the showers in some areas around 9 AM Sunday, but showers will return by late morning.

Tonight’s NBM just available shows an additional 1.5 inches of rain through 7 AM Monday morning—

Tonight’s 00z NBM accumulated rain forecast from 8 PM Saturday through 8 AM Monday. (Click on image for a larger view.)

Incredibly, the remnants of Ophelia may keep showers with us much of Monday and there’s even a chance of showers on Tuesday.

Are the Phillies going to play today?

Updated Sat 09/23 @ 3:52 PM — Despite the weather, the MLB app says the Phillies will play this afternoon. Here’s the current radar at 3:41 PM—

Current radar at 3:41 PM Saturday. (Click on image for a larger view.)
Saturday Storm Update

Updated Sat 09/23 @ 12:12 PM — Don’t be fooled by the breaks of sun we’re seeing now due to ‘dry slotting’. There’s plenty of rain and wind on the way.

Water Vapor image showing ‘dry slot’ moving in from the southeast. It won’t last. (Click on image for a larger view.)

Updated Sat 09/23 @ 11:56 AM — As promised here is the latest GFS model, just available.

The GFS forecast position of the surface and upper low pressure at 8 AM Sunday—

GFS axis of heaviest rain on Sunday is much further west (white box) than previous forecasts which had the heaviest rain through Philadelphia. (Click on image for a larger view.)

This morning’s models continue with a similar forecast as those posted earlier with some differences—

Similarities:

  • Rain continues through Sunday.
  • Highest wind gusts to occur this afternoon and evening.
  • Model Position of upper low on Sunday is fairly similar.

Differences:

  • Axis of highest rainfall is further west with the GFS

I’m sticking with the HRDPS and NBM location of heaviest rain posted below.

Updated Sat 09/23 @ 10:11 AM — Latest (12z) NBM shows the expected additional rainfall forecast from 8 AM today through 8 PM Sunday evening—

Add these amounts above to the amounts from the MRMS graphic immediately below to get a handle on the total rainfall expected from this storm. (Click on image for a larger view.)

Updated Sat 09/23 @ 10:00 AM — Through 9 AM today, here’s the estimated rainfall received, based on the MRMS—

Received rainfall, MRMS estimated at 9 AM today. Contours are in mm. 25.4 mm = 1 inch. A large gradient exists in rainfall northwest of the city. Most models predicted this for today. (Click on image for a larger view.)

Updated Sat 09/23 @ 9:17 AM — I failed to mention with this update that at least half the rain from this storm will fall on Sunday, the other half today, Saturday.

Updated Sat 09/23 @ 8:54 AM — Ophelia has made landfall and is now a strong low pressure system. Here’s the current MRMS radar image with RAP model jet level windstream contours—

This morning’s 7:32 AM MRMS radar image with superimposed RAP Model streamlines. (Click on image for a larger view.)

The remnants of Ophelia are expected to curve back towards northern Delaware, as its circulation throws more moisture over our region.

No model will exactly predict the total amounts of rainfall in all locations, but I’m going to hang my hat on the HRDPS as a reasonable forecast—

Canadian HRDPS (06z) total rainfall forecast through 2 AM Monday morning. (Click on image for a larger view.)

Current NBM wind forecast meteogram for KLOM (Wings Field, Blue Bell PA

Here’s the NBM wind gust forecast for our region at the time of the scheduled Phillies game—

The next models, particularly the GFS, will become available about noon. I’ll update shortly thereafter.

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.)
Philadelphia Weather Outlook

WEEKEND WEATHER PREVIEW

#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.