10-07-24 00z HRRR total rainfall for tonight. (Click on image for a larger view.)
Every high resolution model has this line of storms falling apart by the time it gets to Philadelphia. I’m going with the models, not the radar. We’ll see what happens.
I often chuckle when the TV weather people too frequently use the expression “I’m tracking the storms”. Weather is dynamic, not a train. On this blog, I avoid that expression like the plague.
Hurricane Milton Update
Posted Sunday 10/06/24 @ 3:14 PM —The latest model guidance is forecasting a major hurricane for the west coast of Florida. There is some question about the timing and exact point of landfall, but the intensity looks to be at least a Category 3 or likely a Category 4 storm.
The latest GFS has a northern track, further north than several other models—
Milton looks to be a fast moving but dangerous storm.
Sunday Forecast Update
Posted Sunday 10/06/24 @ 8:55 AM — While some of the lower resolution global models (GFS, ECMWF) still show a line of showers after midnight in our area from a cold front, the higher resolution models (HRRR, RRFS, NAM-NEST, HRDPS,) show very spotty rainfall with low or no rain accumulations in many areas.
Here’s the NAM-NEST forecast total rainfall —
10-06-24 0tz NAM=NEST total rainfall Sunday night (Click on image for a larger view.)
Here’s the HRRR total rainfall forecast for tonight—
10-06-24 06z HRRR forecast rainfall for tonight (Click on image for a larger view.)
Either way, not much in the way of rainfall. The reasons are discussed below.
Hurricane Milton
Posted Saturday 10/05/24 @ 7:55 PM — A new tropical system has developed in the Gulf, likely to intensify and be named Hurricane Milton.
Those following this blog know that the ECMWF-AIFS has been forecasting this development and track for days. While I hadn’t posted the German ICON model, it too was an early forecaster of this system.
The several runs of the GFS have jumped on board with a forecast track that would affect areas recently hurt by Hurricane Helene.
Here’s the latest GFS with a central pressure of 954 mb, likely at least a Category 2 , possibly Category 3 storm —
Today’s 18z run of the GFS. Forecast time is 7 PM Wednesday Central pressure 954 mb (Click on image for a larger view.)
The latest German ICON is further south and slower —
Today’s 18z German ICON model forecast for 7 PM Wednesday. (Click on image for a larger view.)
This morning’s ECMWF is a bit further south (as is the Canadian Global) with this storm—
Todays 12z ECMWF forecast for 7 PM Wednesday. Central pressure 969 millibars. (Click on image for a larger view.)
The model that has been forecasting this for almost a week, the artificial intelligence/machine learning model has a track further south and a bit faster with landfall—
Todays’ 12 ECMWF-AIFS forecast for 7 PM Wednesday (Click on image for a larger view.)
Hurricane Tracks often change and I expect changes in these model forecasts. But a strong system to affect parts of Florida looks high probability.
Update Sat 10/05 5:38 PM — Watching the Phillies game and “doing the weather”. The latest models do show a hurricane at least Category 2 moving into central Florida from the western Gulf. More details after the game
Originally Posted Sat @ 12:27 PM — —Beautiful weather for this weekend. The chance of rain has significantly diminished for our area for Sunday night.
Why are we not getting any rain?
People have asked why we’re not getting rain. The reason is a persistent lower and upper level high pressure system, that both blocks the rainfall and results in downward vertical motion in our area.
More importantly, this persistent high pressure has caused the jet stream to be to our north, resulting in upper level downward motion unfavorable for rain in our area. My conjecture is the global warming has caused the resulting warmer air mass to be larger resulting in a more northern jet flow, along with a smaller air mass of colder air to our north.
As a result, we’re in the in an area of both upper air divergence and the we’re also in the “right exit region” of the jet streak.
Here’s the latest HRRR. Notice the increasing divergence of heights of the 500 mb winds resulting in downward motion and diminishing chance of rain in our area. (Click on image for a larger view.)
Additionally, we’re located south of the jet streak, specifically in the right exit region, also resulting in downward motion unfavorable for rain in our area—
The right exit region has downward motionThe right exit region 2 AM Monday morning. Downward motion in our area. The terms entrance and exit regions are very confusing and not intuitive. (Click on image for a larger view.)
Here’s the HRRR predicted total rainfall for Sunday night. The upper level divergence and position of the exit regions affect our rainfall —
Total rainfall expected Sunday night into Monday. Little to no rain again for us! (Click on image for a larger view.)
I’ll be updating this page about the the likely hurricane to affect Florida later today. (It appears the AI model of the ECMWF has been the first to identify the likely storm. I should note that the German ICON model has been forecasting something similar for several days. )
Posted Friday 09/27/24 @ 10:37 AM — Hurricane Helene will become merged with an upper low today, as a moist east-southeasterly flow in overruns an upper ridge in our area, creating a warm-front type scenario. Here’s the current water vapor image depicting the current conditions—
Friday morning’s Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) potential vorticity (fine violet contours) with superimposed MRMS RADAR. I’ve drawn the pseudo-warm front to depict the moisture over-running the ridge at the surface. Philadelphia is red circle. (Click on image for a larger view.)
The warm front won’t make much progress moving north of our area Friday. We’ll have some heavier rain Friday evening and night.
Drizzle showers and fog are likely to continue through Saturday morning.
It’s possible that some brightening skies poke through Saturday mid day. but most models keep us cloudy and wet.
More clouds and showers likely for Sunday and possibly Monday.
The combined system may spawn a secondary coastal low for rain on Tuesday.
Hurricane Helene Update -Early Weekend Outlook
Posted Thursday 09/26/24 @ 4:32 PM — Hurricane Helene is expected to reach landfall about 8-10 PM in the Big Bend area of Florida, perhaps just east of Tallahassee. It’s then expected to move rapidly northward and then northwestward to be incorporated into the upper closed low pressure system, while some of the moisture is flung northeastward towards our area—
4:30 PM Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) potential vorticity (fine violet contours) with superimposed MRMS RADAR. Hurricane will merge with upper low (L) White arrows path of the hurricane; Violet arrows path of moisture from the combined system. (Click on image for a larger view.)
Several days ago, it appeared that an upper ridge over our area would block the moisture and rain from this system from our area. It currently appears that our area will have clouds and showers Friday through Sunday and possibly into Tuesday.
Helene Update- Early Weekend Outlook
Posted Thursday 09/26/24 @ 10:12 AM — It appears that Hurricane Helene will hit the coastline of Florida, just east and south of the Big Bend between 8PM and 10 PM EDT. Forecast central pressures are in the 958 mb range, suggesting at least a Category 3 storm.
Wind gusts over 100 mph are forecast quite a distance from the storm’s eye—
06z GFS Wind (wind barbs) /WIND GUSTS (shading) forecast for 10 PM EDT Thursday. (Click on image for a larger view.)
It’s appearing increasingly likely that some moisture and resulting rainfall from from this system and its merger with a closed upper low will overspread the Philadelphia area on Friday and Saturday. This to occur despite the persistent blocking ridge which is forecast to retreat. Details likely to change. I’ll update later today.
Thursday – Saturday & Hurricane Helene Update
Posted Wednesday 09/25/24 @ 1:38 PM — Hurricane Helene continues on a track to be a major hurricane. It is forecast to merge with a closed upper level low pressure system in the Midwest with some of it’s moisture moving up against (and slightly over) a high pressure ridge that’s over the Philadelphia area by early Saturday morning.
ECMWF forecast for Thursday 5 PM through Saturday 5 AM. (Click on image for a larger view.)
It appears that by Saturday, some moisture over-running the ridge in our area will bring additional rain as moist tropical air moves in and over us. This tropical air is circulating up from the closed upper low in the Midwest.
ECMWF forecast for Saturday 5 AM. Note the 760 thickness line (orange) , usually seen during heat waves in the summer, approaching our area, associated with tropical air.
For our area, we’ll be under the indirect influence of the circulation around this, almost stationary upper closed low in the Midwest Thursday through Sunday. We’ll continue to see much needed periods of rain.
Latest 12z GFS shows some tropical moisture being spun into our area by the closed low on Thursday. (Click on image for a larger view.)
Currently, much of this rain will fall to our west, but the lack of predictability of both the closed low and the hurricane will make for a changeable forecast with below average confidence. Stay tuned.
Wednesday Forecast
Posted Tuesday, 09/24/24 @ 9:41 PM— A disturbance will approach us from the southwest on Wednesday, unrelated to the moisture associated with developing hurricane Helene. Anyone hoping for a good soaking rainfall will be disappointed; the model blend (NBM) has as much as 0.35″ falling mostly west of Philadelphia on Wednesday.
Tonight’s 00z NBM total precip through 5 AM Thursday. (Click on image for larger view.)
In contrast, the experimental RRFS has much less rain, especially near the city and eastward, on the order of 0.05″
18z RRFS total precip. (Click on image for larger view.)
As mentioned earlier today, the forecast for the coming days will be below average confidence and above average uncertainty. The scenario of a closed upper low and and an interacting tropical system combines two systems that weather models have considerable difficulty with.
Hurricane Helene
Posted Tuesday 09/24/24 @ 5:41 PM — Sorry folks. I jumped the gun with the hurricane name and incorrectly used the name, Gordon, already used for a central Atlantic hurricane recently. The new Hurricane is Helene. What’s in a name? (Quite a bit!) We now return you to our regularly scheduled programming.
Posted Tuesday 09/24/24 @ 9:35 AM — While not yet officially categorized as a hurricane, Tropical Cyclone 9 (to be called Hurricane Helene} promises to be a major hurricane according to most models. It’s expected to approach the Florida Great Bend area (and near the coast from Tampa northward) early Thursday.
The power of this storm will cause it to remain as a hurricane even when it enters Georgia.
The ECMWF-AIFS has been fairly consistent with its forecast and track for several days. Here’s a graphic I put together to capture its size and track Thursday into Thursday night—
ECMWF-AIFS forecast for Tropical Cyclone 9 ==> Hurricane Helene Thursday morning into early Friday morning. Notice that the storm is forecast to become incorporated in the upper low over Tennessee and the moisture will be blocked from northern movement to our area. (Click on image for a larger view.)
Notice the same high pressure system that has been keeping us with little rainfall will block northeastern movement of the rain associated with Helene.
Here are some official tracks—
Since this scenario involves an upper closed low and a tropical system, it presents a double-whammy for weather models. We’ll see what happens.
As for our area, no change from previous forecast for today, Tuesday. Cloudy, some bright skies and even brief partly sunny intervals mid day and early afternoon. Showers move in later.
Tuesday Outlook
Posted Monday 09/23/24 @ 4:54 PM — Some light showers made it into the Philadelphia area Monday afternoon, and additional intermittent light showers area expected tonight. (There had been uncertainty yesterday regarding the progress of the showers into our area this afternoon.)
Last night’s 00z experimental RRFS accurately forecast these showers.
Unfortunately, the RRFS output has been intermittent, delayed or missing over the past two weeks. The model development group are making improvements. However, recent revisions in the “precipitation physics” seems to have improved its forecasts and has made it worth the wait.
Here’s last night’s RRFS 00z forecast for 3 PM—
00z Experimental RRFS simulated radar/clouds for 3 PM Monday (Click on image for a larger view.)
Here’s the radar at 3 PM—
NEXRAD radar with superimposed MRMS composite at 3 PM (Click on image for a larger view.)
For Tuesday, light showers end around daybreak and much of Tuesday should be cloudy, perhaps with some intervals of sun or bright skies.
Showers return Tuesday night and much of Wednesday. Total rainfall still does NOT look impressive in the immediate Philadelphia area and eastward.
I’m still watching the development of Tropical Storm 9, likely to become Hurricane Helene. The trend has followed the ECMWF-AIFS model fairly well, with a more eastward track affecting the Great Bend of Florida and areas near Tampa and north.
Here’s the latest ECMWF-AIFS forecast for Thursday 8 PM—
12 ECMWF-AIFS forecast for Thursday 8 PM. Some of the moisture outflow gets brought up to our area, according to this model. The regular ECMWF and GFS blocks that flow of moisture here. (Click on image for a larger view.)
An interesting weather week. Stay tuned.
Originally Posted Sun @ 5:34 PM — —This week’s weather will be influenced by low pressure (1) moving in from the west, a developing strong hurricane (2) in the Gulf, blocking persistent high pressure (4) to our north and persistent blocked low (3) in the Atlantic —
09-22-24 12z GFS for Tuesday afternoon Low pressure (1) moving in from the west, a developing strong hurricane (2) in the Gulf, blocking persistent high pressure (4) to our north and persistent blocked low (3) in the Atlantic (Click on image for larger view.)
Monday
Monday will be cloudy, perhaps with some sunny intervals around noontime.
The HRRR has some showers moving in late afternoon and early evening. How far they will get into the city is an unknown, since the HRRR has blocking high pressure building in at the same time—
09-22-24 18z HRRR with blocking high pressure (blue shading). This shunts much of the rain to our south. (Click on image for a larger view.)
The NAM-NEST is predicting most of these showers on Monday are shunted to our south, but some may give parts of our dry area some light showers.
We may finally get a period of rain on Wednesday, as the high pressure system will retreat to the northeast.
Towards the end of the week, the next hurricane (“Helene”) is expected to form and to move inland around the Florida Panhandle or the Florida Great Bend area. according to the ECMWF AIFS. This hurricane could be powerful. Incredibly, our much needed rainfall here may be blocked by high pressure and an upper level ridge again.
There remains uncertainty about this possible hurricane, according to the National Hurricane Center and I may be jumping the gun on the hurricane forecast . Nonetheless, the GFS, ECMWF and CMC Global all predict some strong system.
Today’s 12z ECMWF AIFS forecast for Thursday at 8 PM. Hurricane Helene is expected to form and to move northward from the Gulf. Much of the rain will move to our west and be blocked from our area. (Click on image for a larger view.)
