30 August 2013

Atlantic hurricane season still lacking hurricanes

Today's update on the conditions and activity across the basin can be found on the Washington Post's Capital Weather Gang blog:

Atlantic hurricane season still lacking hurricanes: any sign of a change?

28 August 2013

Remembering Katrina

Today, August 28th, is a day many in the hurricane community will never forget. It was a Sunday morning, and we started the day off staring in disbelief at what had become an enormous Category 5 hurricane sitting in the central Gulf of Mexico - and heading north.

Katrina as a Category 5 hurricane on August 28th, 2005. (NOAA)

It hit Miami, FL three days prior as an intensifying Category 1 hurricane, and strengthened as it crossed over the eastern Gulf. The forecast was, and had been, accurately centered on eastern Louisiana and Mississippi for several days; the big question leading up to that landfall would be the intensity.

For many years, the "New Orleans scenario" was well-known, and had been addressed in practice drills and exercises... it's a very vulnerable city, with many areas situated below sea level. Everyone knew this would be bad; really bad. The NWS forecast office in New Orleans issued the following warning in advance of the landfall:

"MOST OF THE AREA WILL BE UNINHABITABLE FOR WEEKS...PERHAPS LONGER. AT LEAST ONE HALF OF WELL CONSTRUCTED HOMES WILL HAVE ROOF AND WALL FAILURE. ALL GABLED ROOFS WILL FAIL...LEAVING THOSE HOMES SEVERELY DAMAGED OR DESTROYED. POWER OUTAGES WILL LAST FOR WEEKS...AS MOST POWER POLES WILL BE DOWN AND TRANSFORMERS DESTROYED. WATER SHORTAGES WILL MAKE HUMAN SUFFERING INCREDIBLE BY MODERN STANDARDS."

Of course, as dire as that sounds, the end result was even worse. It made landfall on the morning of August 29th... it would become the costliest natural disaster in the history of the U.S. (~$108 billion), and was responsible for nearly 2,000 deaths. The only good news was that it weakened quite a bit prior to landfall, and came ashore as a weakening Category 3 storm (120mph winds) rather than the Category 5 (175mph winds) it was a day earlier. Watch a radar loop of the landfall... and note that the final frame also marks the time the radar there was destroyed.

It generated a devastating 27.8-foot storm surge in Mississippi, and the smaller surge in New Orleans was enough to stress the levees protecting the city beyond their breaking point. Many beachfront communities were erased from the map, particularly in Mississippi.

Observed storm surge generated by Katrina. The peak value in the ">16 feet" category was nearly 28 feet in Pass Christian, MS... the largest surge ever recorded in the U.S. (SURGEDAT)

Later that year, other major hurricanes (Cat3+) made U.S. landfall, wrapping up with Wilma on October 24th when it hit the southwestern Florida peninsula. That remains the last time the U.S. was hit by a major hurricane. I included some details on just how bizarre and unprecedented this span is in my season wrap-up last year (scroll down to the 7th paragraph).

25 August 2013

Last week of August comes with increasing activity

As I eluded to in Friday's update, the tropical Atlantic is primed to start cranking out some storms, especially toward the beginning of September. But even now, a couple areas of interest are brewing: one rapidly organizing system in the southern Gulf of Mexico and another near the African coast.

First, the disturbance in the far southern Gulf of Mexico. This is an African easterly wave that was located back over the Lesser Antilles on the 19th, and got more convectively active on the 22nd. Since then it passed over the Yucatan peninsula and just emerged into the Bay of Campeche recently. It has been surprisingly quick to get organized, and an aircraft reconnaissance plane has been tasked to investigate it later this afternoon. The aircraft could possibly find it to be a tropical storm... if so, the next name on the list is Fernand. Fernand is a new name this year, replacing Felix from 2007's list.

Disturbance in the Bay of Campeche, heading west toward Mexico. (NASA)

Even if it does continue to intensify, its time before landfall is very limited. It's heading generally westward, which brings it over land by this evening. It is already showing up nicely on radar... I have a long radar loop from Alvarado available (Invest 95L). As usual for weaker systems, the largest threat will be heavy rain and flash flooding.

Shifting our attention 5200 miles to the east, a wave has just exited the African coast and though it doesn't look too impressive just yet, several global models do forecast it to get organized over the next several days as it heads W-WNW across the deep tropics. It's coming off at a more typical latitude, centered near 10N 18W, and the environment appears to be favorable for development. I will provide additional details on it as the week goes on.

Visible satellite image of an easterly wave coming off the African coast. (CIMSS)

23 August 2013

Update on activity (or lack thereof) so far this season

With all of the forecasts for an active Atlantic hurricane season, it seems a bit odd that there have been no hurricanes yet, and we're heading into the last week of August. For an update on the conditions and expectations, check out my post on the Washington Post's Capital Weather Gang blog:

Where the heck are all the hurricanes??

16 August 2013

Both Atlantic systems weaken

In the past 24 hours, both Erin and the disturbance near the Yucatan have lost a lot of steam.

The Yucatan system is just now about to enter the Gulf of Mexico, but the surface circulation is devoid of deep convection, and a strong upper-level low to its north is introducing hostile vertical wind shear. In the images below, the left one is an enhanced infrared image which allows you to see the low clouds in yellow and the higher clouds in white... and the right one is a water vapor image, which mostly shows what's going on in the upper atmosphere. I added basic low-level features in green and upper-level features in red for clarity.

Since it is now reduced to just a low-level circulation, it should track more toward the west-northwest, rather than turning toward the north. This shifts the longer-range landfall location to Texas or northern Mexico... but, "landfall" makes it sound more significant than it really is. Wherever it goes, its biggest impact will be heavy rain -- perhaps not even that!

However, if it does head more westward, environmental conditions would improve for the disturbance in a couple days, perhaps allowing it to regain a little organization. The current "worst case" model (which still isn't TOO bad) is HWRF, which strengthens it into a hurricane and shows a landfall near Brownsville on Monday night. Other models are less bullish.

Surface wind (shaded contours) and surface pressure (line contours) according to the most recent HWRF model run. Not a likely solution, but one with a slim possibility, and worth being casually aware of at least.

The key to the evolution of this system will be if it goes more west than north, and if new deep convection can develop and persist near the center. If not, then it can be written off.

Much further east, Tropical Depression Erin is gradually heading into drier air and cooler waters as expected. It is also now reduced to a skeletal cloud swirl centered about 400 miles west of the Cape Verde islands. It would need to hang around for another three days or so until it tracks into a slightly more favorable environment... but still not ideal. Most models dissipate the storm within the next 3-5 days, and track it northward into the north-central Atlantic graveyard.

Tropical Storm Erin west of the Cape Verde islands. (NRLMRY)

For a bit of hurricane history, on this date in 1992, the season's fourth tropical depression formed 700 miles west of the Cape Verde islands. On August 17th, it was upgraded to the season's first tropical storm: Andrew. Seven days after getting named and significant intensification, the tiny Category 5 hurricane plowed head-on into Florida, just south of Miami. It is one of just three Category 5 hurricane landfalls on the U.S., and the most recent. Do you know the other two??

15 August 2013

Tropical Storm Erin forms, Caribbean disturbance heads into Yucatan

Today's update can once again be found on the Capital Weather Gang blog... thanks for reading and sharing!

Tropical Storm Erin forms, Caribbean disturbance heads into Yucatan

14 August 2013