Tag Archives: forecast models

Fall is in the air, but tropical season isn’t over yet…

Something happened last night that hasn’t happened for several months — I felt cold.

Fall is definitely on the approach. While I won’t rule out one last resurgence of warmth in the next few weeks (this typically happens in Charleston, we can’t transition nicely into seasons here at all), we’re entering the second of the two periods of the year where Charleston’s weather is incredibly gorgeous. I’m talking high 70s to low 80s for highs, and low to mid-60s for lows.

While fall is generally more tame than spring severe weather-wise, there can still be elevated levels of severe weather, because the setup is similar to spring: strong cold fronts running into warm air, causing lift and storm formation. Now that we’re seeing fronts again, there could be some decent storms at times.

In the next week, at least, we’ll be keeping some cloudiness around with a chance of showers. There’s a disturbance southwest of here that’s been consistently kicking up some rain on long-range radar.

Hurricane season isn’t over yet: Invest 93L out there

Thankfully, the tropics have been much quieter since Ike roared ashore in Texas. However, a disturbance is trying to get it together in the Atlantic; the Hurricane Center has dubbed this one 93L for now and are watching it for development. As the model spread indicates, there is no shortage of computerized opinion about what this one’s going to do. The HWRF and GFDL models develop it and take it northward; GFDL curves it out to sea, but HWRF seems to keep it hanging around the islands and weakening it. Again, it’s early as heck, and it’s tough to say what will happen. Jeff Masters seems to think that this one will gradually get it together. Again, it’s always worth watching — a tough sell to a hurricane-fatigued populace, for sure.

In the meantime, enjoy the weather out there — it’s pretty gorgeous, if not a bit on the cloudy side.

8am: Increasing divergence ahead of landfall

8am Hanna Computer Models

Here’s the 8am model runs. Note the increasing amount of divergence ahead of Hanna’s landfall. There’s still reasonably strong agreement for the Horry County landfall scenario, but I would not be surprised to see the track jog west a bit more before it’s all said and done.

The 8:00 advisory slows Hanna’s forward motion down ever so slightly (to 18 MPH instead of 20). It’s still headed northwest. Winds are still 65 MPH, but the pressure is down a bit more. Satellite imagery is indicating that the shear has backed off some; note the gigantic plume of convection trying to wrap itself around the center. A hurricane at landfall is reemerging as a possibility.

Stay tuned…

11 PM: Hanna begins northwest turn; watches likely tomorrow

Tropical Storm Hanna 11PM Advisory 09/03:  Satellite Photo

The 11PM advisory is now out on a steadily reorganizing Hanna. Winds remain around 65 MPH, and pressure is sticking around 989 millibars. The Turn has really started to happen, as NHC states forward motion is north-northwest at 13 MPH.

The Track

Tropical Storm Hanna 11PM Advisory 09/03:  Track + Uncertainty Cone

The track seems to have shifted a bit more leftward before landfall; there’s still a fair bit of uncertainty. In the discussion, NHC acknowledges low confidence in the track, citing some spread in the forecast models.

Tropical Storm Hanna 11PM Advisory 09/03:  Forecast Models

There’s good consensus for a turn to the north and then the northeast; the big question is where it will happen. There’s decent consensus heading toward Wilmington, but there’s spread on the western periphery of the consensus — including a HWRF model that generally gets a fair bit of weight from NHC forecasters — hence the uncertainty and the slight leftward jog in the track.

NHC is saying that hurricane watches are likely for a “large portion of the southeast US coast” by tomorrow morning. It’s probably safe to assume that we in Charleston will be included in this watch.

It’s worth noting that the storm will be relatively short-lived; it’ll be increasing in forward speed throughout its approach. In Charleston, it’s likely that Hanna will have largely cleared the area by Saturday night. This is good for reducing the threat of severe flooding. There will still be heavy rains, but at least they will be short-lived.

Effects

Charleston should start feeling effects from Hanna as Friday wears on. As it gets closer, winds will increase. I’ve been able to use an experimental forecast wind field product as a decent guideline for what we might see here.

Tropical Storm Hanna 11PM Advisory 09/03:  Forecast Wind Field

The forecast says that we’ll see some of the worst of the weather Friday night into early Saturday morning, as the center passes within 75 miles or so of Charleston. Sustained winds of 58 miles per hour or greater — as indicated by the purple shading in the map above — are possible for a brief period. As mentioned above, rain totals will probably hit 6″ in some places, but this won’t be a storm that sits and spins and dumps 30″ of rain like a Fay over Florida.

Again, a lot of this is contingent on something resembling the current track holding. There’s more time for stuff to wobble back and forth, and Charleston is still in the cone of uncertainty, so there’s still stuff to watch. However, the direct strike scenario is looking less and less likely.

Closures, etc.

Keep an eye to media outlets and other sources for closure information in the Charleston area tomorrow, as I expect most of those closures (or lack thereof) would be announced during the day. A good resource for this is the @news2 Twitterstream.

Check out Lowcountry Bloggers’ Storm Buzz

The Lowcountry Bloggers roundup site has launched Storm Buzz, an automated feed of hurricane-related posts from the Lowcountry blogosphere. This is a good one-stop resource to see what Charleston bloggers have to say about Hanna and Ike.

Speaking of Ike…

Ike exploded into a dangerous but equally gorgeous Category 4 storm during the day Wednesday. It’s in a perfect environment for strengthening and could be a 5 before it’s all said and done. It’s expected to weaken to a 3; tentatively, it’s headed to the Bahamas, but there’s a lot of spread and uncertainty. It could recurve out into the sea — which would be ideal, of course — or it could threaten the U.S. within the next five or so days. Ike is one to watch because it’s expected to retain major hurricane status as it traverses the Atlantic, with fluctuations in intensity characteristic of huge storms.

For now, though, all eyes will continue to be on Hanna as she makes her move toward the coast. I’ll have more in the morning, probably shortly after the 8am advisory unless there’s a major shift in track that needs immediate attention.

Coverage Continues

Another video briefing will be broadcast at about 9:15 PM, with a roundup of the day’s information and hopefully a better fix on what Hanna’s going to do. She’s still got a history of behaving badly and needs to be watched closely.

Coverage will be more frequent as conditions deteriorate; I’m planning on bringing in additional folks to assist with coverage. Additional streams are planned for as long as power is viable. Now’s the time to follow @chswx and my own personal Twitter account for information and accounts of the storm, too.

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. :)