Tag Archives: computer models

And ’round and ’round we go…

Tropical Storm Hanna: 5am

Hanna continues to frustrate folks here in Charleston from just northwest of Haiti as it does a little loop-de-loop (it’s already completed one) over the water, waiting for the high pressure system to build in, pick it up and whisk it off to the northwest. The good news is that it’s still on a slow weakening trend; this morning’s satellite image, depicted above, has her looking like a flat-out mess. The thunderstorms are fairly well-separated from the center; it’s amazing it’s maintaining 60 MPH winds as it interacts with Hispaniola.

Because The Turn hasn’t happened yet, we still are stuck in a wait-and-see pattern. This is frustrating because as NHC’s stated before, we won’t have any idea of exactly where landfall will happen until this thing starts to get going.

The 8am model runs showed a wild rightward shift in almost every model, probably as a result of Hanna’s eastern motion. Time will tell if this shift is anomalous or shows more of a permanent rightward trend. The 2am models started to demonstrate more rightward movement, but the 8am ones are the first time that I’ve seen the HWRF and GFDL models tack as significantly northward as they have.

Tropical Storm Hanna: 5am

The official forecast should look pretty familiar to you at this point, if not a smidge more rightward than previous tracks. Will be interesting to see what 11am brings.

I won’t be blogging all that often today; keep an eye to the Charleston Weather Twitter for updates throughout the day. I’m going to do a video briefing at 9:30 tonight; it won’t last too terribly long unless there are significant changes to discuss (and I’m willing to bet there might be). Back to waiting!

Wait and see continues…

The wait and see game continues with Hanna at the 11PM advisory. The storm’s back to being virtually stationary, drifting eastward every now and again, but movement is not very pronounced. NHC continues to list Hanna’s intensity at 65 MPH; however, this could be generous. Check out Hanna’s satellite appearance.

Tropical Storm Hanna at 11PM 09/02:  Satellite

Here’s what the Hurricane Center discussion has to say:

THE CLOUD
PATTERN HAS CONTINUED TO DEGRADE…AND IT IS POSSIBLE THAT HANNA
HAS WEAKENED EVEN MORE. HOWEVER…WE WILL KEEP THE INITIAL
INTENSITY AT 55 KT SINCE ANOTHER AIRCRAFT IS SCHEDULED TO
INVESTIGATE THE STORM AROUND 0600 UTC.

This apparent weakening is undoubtedly good news and appears to have gone on a little longer than previously expected. (We’ll take what we can get here.)

Back on Track?

Tropical Storm Hanna at 11PM 09/02: Forecast Path w/ Cone

The forecast path has not changed much during the day. The angle of approach has been adjusted somewhat, but NHC has been very careful not to alter the path until Hanna finally starts the northwestward turn. Only after the turn begins will landfall points even begin to get a smidgen clearer. One thing to notice is that the updated track is a bit slower (for the moment, at least), pegging landfall now for later on Friday night versus in the afternoon. This is definitely something that could fluctuate depending on when Hanna starts moving and how fast it’s accelerated.

Tropical Storm Hanna at 11PM 09/02: Forecast Models

The computer models want to tell a different tale, though. After a brief jog to the west, they’ve since started trending rightward again, likely as a result of Hanna’s eastward movement during the evening. The models bear out a variety of scenarios; some, like HWRF, favor the southerly track, while GFDL, which has consistently veered more to the north, currently likes Isle of Palms. There’s significant agreement, though, for a landfall near Myrtle Beach. Some consensus is also building for an alternate clipping of the Outer Banks, though I’m not sure if that would come to pass as the HWRF and GFDL models have been exceptionally reliable. It’ll be interesting what will come out of the models when the recon data is taken into account. (NHC lists the next recon plane as going in at roughly 2 AM EDT.)

Impacts

It’s still too early to tell — besides pretty decent amounts of rain and some elevated winds, probably to tropical storm force at times — what impacts Hanna will have on the area as the landfall location is still anybody’s guess. Using the current landfall location, though, I’m able to use an experimental wind field forecast product to give a general idea of what windspeeds to expect.

Tropical Storm Hanna at 11PM 09/02: Estimated Wind Field

The gray field is tropical storm force winds; the purple field are stronger tropical storm force winds up to 73 MPH. No hurricane force winds are depicted yet; if in fact Hanna makes landfall as a Category 1, expect those hurricane force winds (74 MPH or greater) to be concentrated about 20-25 miles to the northeast of the center. Intensity, storm size, etc. are still very touch and go at this point, so don’t read too terribly much into this; however, the estimation does show that a great deal of the state, including points as far west as Columbia and Augusta, could see tropical storm force winds for a time. Again, this should be interpreted as a general idea, and it’s quite possible a lot could change.

Closures, etc.

No word on any closures yet. The Charleston County School District has established a Hanna information page which will update as schedule decisions are made. Dorchester District 2 posted an inclement weather policy, but no closing information as of yet. I’ve not seen anything similar for Berkeley or Dorchester 4. Keep tuned to the local media outlets for up-to-the-minute closures and cancellations information.

More in the morning when the recon data is in; hoping that my getting some sleep will persuade Hanna to make a decision one way or the other so we can start trying to figure her out with some effectiveness. :)

Tonight’s Hanna briefing

Tonight’s briefing covered the latest on a ragged-looking Hanna, which has been erratic most of the day. I focused a lot on the models and a lot of the variation throughout today; things are still quite uncertain. I’m holding out hope that the 11PM advisory will start to shed some light but that might have to wait for a few more hours.

Hanna’s definitely not moving much, and its satellite presentation is very poor. It looks like it’ll be weakened even further with the next advisory…only time will tell. I’ll have more after 11…

2PM: Hanna The Meanderer…for now

Apologies for the later post; the day job has been hectic with storm stuff as well.

Tropical Storm Hanna’s been caught in something of a steering purgatory this afternoon; it continues to rain very heavily on the Turks and Caicos. As of the 2PM advisory, it’s moving SE at 2 MPH. We’re all awaiting the ridge of high pressure to build in and take it away — but it’s all a wait and see, still.

Intensity Rollercoaster

Hanna’s also been in a weakening trend; Gustav’s outflow has been negatively affecting it most of the day, having a great deal of its northwestern quadrant sheared off, helping to weaken the storm to tropical storm status earlier in the day. It’s held on as a 70 MPH tropical storm, so when the shear lets up, there won’t be much inhibiting it to becoming at least a minimal hurricane again.

This weakening has thrown a wrench in a lot of the forecast, though. The 11AM forecast discussion demonstrates significant uncertainty in the intensity forecast — it could barely hang on as a Category 1, or break free from the shear and blossom into a Category 3:

HOWEVER…GIVEN THE PRESENT LACK OF
ORGANIZATION…IT IS DIFFICULT TO KNOW HOW MUCH STRENGTHENING IS
POSSIBLE. THE NEW OFFICIAL FORECAST IS LOWER THAN THE PREVIOUS
ADVISORY BUT SHOWS HANNA BECOMING A CATEGORY ONE HURRICANE IN ABOUT
36 HOURS. IT SHOULD BE NOTED THAT THIS IS A LOW CONFIDENCE
FORECAST. IN FACT…IF ONE CONSULTS THE WIND SPEED PROBABILITY
PRODUCT INCLUDED IN THIS PACKAGE…IT CAN BE SEEN THAT THERE IS
NEARLY AN EQUAL PROBABILITY OF HANNA BEING A TROPICAL STORM OR
HURRICANE AT DAY 3.

A recon flight should shed much more light on Hanna’s structure; a flight’s scheduled for this afternoon and it probably is on the way in as I type. Here’s hoping that information is reflected in the 5PM.

Track Thoughts

The 11am advisory shifted the track back westward a little bit. Here’s the NHC’s map:

The NHC forecast track splits two groupings of model guidance down the middle. Here’s the high-carb meteorological pasta as of 3:15:

Computer Models at 3:00 Tuesday

One camp — with tighter agreement, I may add — takes an even more westward tack, bringing the center of Hanna onshore to central Georgia. Notably, the GFDL and HWRF models favor this scenario, with the GFDL taking a Category 3 just north of Jacksonville Friday. HWRF is a bit weaker, expecting a Category 2 storm. The other camp favors a Charleston-to-Myrtle Beach swath primarily. It’s a bit more divergent than the other two camps in terms of exact points, but remember, it’s still too early to get caught up in little jogs here and there. NHC has not adjusted the track much in part because Hanna’s size and intensity, as well as where it begins its movement from — remember, the storm has been meandering aimlessly southeast — has some bearing on how much and how quickly the expected high pressure will influence it.

Emergency Preparation

I caught Raymond from News 2’s tweets from the Charleston County EOC meeting. EOC has switched to OPCON 3, which activates the emergency operations center and indicates that an emergency situation is imminent. Mayor Riley is giving a press conference at 3:30 this afternoon; I recommend keeping an eye on News2’s Twitter. I’ll be watching that and will retweet big nuggets of information accordingly on both @chswx and @jaredwsmith.

Don’t forget about the video briefing tonight, tentatively scheduled for 9:15 PM. Sorry it’s so late in the night; I have obligations (read: class) to attend to from 7:00 to 8:15. This will give me an opportunity to review the 8PM advisory and break things down a bit better.

A special hello to those of you who came from The State — thanks for stopping in, and thanks to The State for syndicating this blog on their Web site! I hope folks are finding this useful; I know I’m enjoying doing it. :)

5am: Hanna Still Drifting

Not much on Hanna has changed since the 11PM advisory; it’s still at 80 MPH drifting west at 2. What we’re waiting for is that turn to start, and that’s not expected to happen until tomorrow. The sooner it begins turning, the more northward the track will likely go.

One thing that bothers me from this morning’s advisory is this passage from the NHC discussion:

It is important to note that
Hanna is expected to continue to intensify…or at least remain
steady…until landfall occurs between 84 and 96 hours…rather
than appear to be weakening like some automatic intensity plotting
software may show. In fact…by 84 hours Hanna could be a major
hurricane.

The GFDL model has indicated for the past several days that this could hit minimal Category 3 strength before landfall, and for the first time it appears NHC is supporting this theory. Intensity is a struggle to predict; this deserves further watch as a potential Category 3 strike changes the game dramatically in terms of evacuations and other preparedness steps.

Here’s the full run of model plots from overnight. You’ll see two clusters; one favoring the Savannah track, and one favoring the northerly track into Charleston. GFDL also seems to want to target Myrtle Beach:

All Forecast Models -- Hanna -- 6am

Here’s one that focuses on the more tropical-oriented models; call it the “low-carb” spaghetti plot if you will. Note a bit more spread with these on the orders of hundreds of miles — this is significant, and why the cone of uncertainty is still so wide:

Significant Model Runs -- Hanna -- 09/02/2008 5am

And, for completeness’ sake, the largely unchanged official forecast, which still targets a Category 2 landfall now over Hollywood/Ravenel (but this is still minutia; still a long way to go to determine specifics):

Hanna Projected Path, 5am Advisory 09/02/2008

I’m hoping later today we’ll start to see what a projected wind field may look like over Charleston (and also hoping that maybe this thing will jog out to sea, but that’s not looking too likely at this point). Today is a good day to commence your preparations; my advice is to prepare as if it’s a medium Cat 3 at landfall. While that might not end up being the case, it’s best to over-prepare at this point. If in fact the higher intensity does begin to bear out, you may need to start thinking of evacuation plans depending on where you are.

I’ll be doing a video chat with the 5PM track and 8PM information at about 9:15 tonight. Stay tuned…it’s just now getting interesting.

Hanna trending rightward

The 11PM advisory is out on Hanna. She’s holding steady at 80 MPH; pressure’s down a couple millibars to 978, and this storm is very, very stationary, causing a lot of problems on the Turks and Caicos with the potential for deadly mudslides due to the copious amounts of rain being dumped on the area.

Hanna Forecast Track, 11PM 09/01

The forecast track has shifted eastward and now predicts a landfall Friday afternoon around the Charleston metro or just a teeny bit north. I must reiterate that this scenario is very uncertain and could all change by the time we wake up tomorrow morning.

I’ve noticed this eastward trend progressing throughout the day; this morning, landfall was projected south of Savannah; at 5PM, landfall was shifted to the border with a hard turn right up through the gut of SC; now, another eastward shift takes it into Charleston. This is a curious development; I’ll get into that in a moment. First, here’s some explanation from the NHC discussion (links to models added by me, where appropriate):

AS HIGH PRESSURE DEVELOPS
OVER THE WESTERN ATLANTIC OVER THE NEXT 2 TO 3 DAYS…A
NORTHWESTWARD TRACK FOR HANNA IS EXPECTED TO DEVELOP. WITH THE
EXCEPTION OF THE UKMET…THE MODEL GUIDANCE IS REMARKABLY WELL
CLUSTERED. THE OFFICIAL FORECAST IS ADJUSTED SLIGHTLY TO THE EAST
OF THE PREVIOUS ADVISORY AND IS ONLY SLIGHTLY TO THE LEFT OF THE
GFSGFDL…AND HWRF.

Here are the latest spaghetti plots for those of you who are into meteorological pasta:

Hanna Models -- Overview -- 11PM 09/01

And a close-in view of the plots as they cross over Charleston:

Hanna Model Plots - Close In on Charleston

I do find it interesting that they’re leaning on the GFS, GFDL, and HWRF so much; as the spaghetti indicates, there’s still plenty of support for the more leftward solution. It probably has to do with the reliability of GFDL lately, and the fact that GFS trended more leftward to match up with it; but this is still an interesting development. The morning runs will be good to watch to see if more things come into alignment with this rightward track. Again, the cone of uncertainty is quite wide, and it’s still important for everyone from Miami to Norfolk to keep close tabs on this one.

More in the morning…