Saturday, June 30, 2012

Tropical Storm Debby Storm Surge Observations

Tropical Storm Debby formed in the Gulf of Mexico on June 23, 2012. The system slowly tracked to the northeast, stalling several times south of the Florida Panhandle. The system continued to track northeast, however, before making landfall north of Cedar Key, FL on June 26.

Debby produced severe flooding in many parts of Florida. In some areas the flooding was completely due to heavy rainfall, while in other areas it resulted from a combination of rainfall and storm surge. For example, portions of the Tampa/ St. Petersburg area flooded as water from torrential rains was slow to runoff due to elevated bay levels from storm surge.

Yesterday, world-famous coastal scientist Mike Bitton emailed me for Debby's surge obs, and I was ashamed to realize I didn't know what to tell him. So I dug a bit this morning and came up with some numbers. I hope if I can keep Mike on my good side he'll go cycling with me someday!

 These are highest surge obs that I estimated from NOAA Tides and Currents graphs. The visual estimation is probably accurate to within 1/10 of a foot, however, these numbers are listed as preliminary on the NOAA Tides and Currents website. All water elevations are height above Mean Sea Level (MSL).

Selected storm surge observations for Tropical Storm Debby:

Location                      Estimated Height (feet)       Date of High Water Obs
Fort Myers, FL            3.05                                     6/25
Old Port Tampa, FL    4.00                                      6/26
St. Petersburg, FL       3.55                                      6/26
Port Manatee, FL        3.3                                       6/26
Clearwater, FL            3.05                                     6/25
Cedar Key, FL            4.5                                       6/26
Apalachicola, FL        3.5                                       6/24-25
Panama City, FL         1.7                                       6/24
Pensacola, FL             1.9                                       6/25
Dauphin Island, AL     2.2                                      6/25
Mobile State Docks    1.7                                      6/25
Pascagoula, MS          2.3                                      6/25
Bay Waveland, MS      2.4                                      6/24
Shell Beach, LA          2.7                                      6/24
Pilots Station E, LA    2.3                                      6/25
If you have a surge observation you'd like to include on this list, please comment on this post, or email me at:

Hurricane Hal

Sunday, June 24, 2012

NHC Shifts Track East - Debby Likely a Florida Storm

The National Hurricane Center shifted the forecast track for Hurricane Debby farther to the east. The present forecast takes the center of circulation nearly due north- towards Panama City, FL, although uncertainty regarding track and intensity still exists.

Former tropical cyclones that have followed a similar track have produced peak surge levels near Apalachee Bay south to around Cedar Key. High water levels in these storms often are observed near Tampa Bay/ Clearwater as well.

It's hard to find a tropical storm that tracked so slowly north in this area. Tropical Storm Alberto, however, did take a somewhat similar track at a slow pace, however, in 2006.

Tropical Storm Alberto track map. Source: Unisys Corporation

Surge info for Alberto:

Peak surge was approximately 6 feet in Homosassa, FL according the Source 1 description below:

Source 1:

Numerous houses received flood damage as two feet of water covered the road to downtown in Levy County, FL. Storm surge flooding near Homosassa, Citrus County put 3 ft of water into a restaurant and damaged 20 homes.

Source 2:

Surge Info:
Table 2 provides storm surge levels above normal astromical tides. The highest water level in Cedar Key was 4.27 feet, while a high water level of 4.92 feet was reported in Dixie County.

According to NOAA Tides and Currents, water levels at Cedar Key have been as high as 3.77 feet above normal this evening.

Stay tuned to your favorite weather information outlets for updated forecasts on this storm, and check back to this blog in the morning and evening for information about Debby's surge and possibly some surge history that relates to this storm.


Clarification about Tropical Storm Debby

I'd like to add a few words of clarification about Tropical Storm Debby. I pulled surge data from a few historical storms that had similar tracks and intensities to the National Hurricane Center forecast. However, I cannot stress enough that models disagree with the track and intensity of this system. Some models forecast a turn to the west, while others a curve to the east. Most forecasts include a short-term drift to the north.

In light of these uncertainties, all interests from Texas to Florida should pay close attention to this storm. Also, check back with this blog often, as I may pull historical examples of surge events for the northern or eastern Gulf Coast. I'd like to point out as well that I'm in no way forecasting or predicting surge levels with Debby, just trying to provide some historical context from storm surge climatology.

It does look like most models predict Debby to slowly drift northward, which is why forecasts keep a persistent east wind in place across much of the northern Gulf. Historically, prolonged east winds have piled up water along the eastern levee of the Mississippi River, in the Lake Borgne/ Shell Beach area, Lake Pontchartrain and even in the Mississippi Sound.

Tides are also running above normal in the Florida panhandle and western coast of Florida. Water levels at Apalachicola have been running from 2 to 2.5 feet above normal, according to NOAA Tides and Currents. Most of the rain and surge impacts with this system have occurred in Florida so far.

Check back for updates.


A Look Back at Hurricane #2 in 1940

The National Hurricane Center continues to forecast Debby to move west after a slow drift to the north. However, they have increased the intensity forecast as Debby passes south of the LA Coast. In fact, the latest forecast places Debby as a hurricane off the coast of Louisiana as it slowly moves westward on Wednesday and Thursday. However, as previously mentioned, much uncertainty still exists between various models, so the confidence of this forecast is marginal.

Source: The National Hurricane Center

Hurricane #2 from the 1940 season provides an interesting comparison if Debby does indeed strengthen into a hurricane off the LA Coast.This storm strengthened from a tropical storm to a hurricane south of Grand Isle, LA, then slowly tracked WNW before making landfall near the TX/ LA border.

Hurricane #2 from the 1940 hurricane season. Yellow = tropical storm, red = hurricane. Source: Unisys Corporation

The U.S. Army Corps document, History of Hurricane Occurrences along Coastal Louisiana, provides interesting insight into the 1940 surge event. Although the storm made landfall near the TX/ LA border, the highest observed storm tide value was observed far from the landfall area. The peak storm tide was 6.4 feet at Frenier, LA, on the southwest shore of Lake Pontchartrain!

Some storm tide observations, provided on page 29 of the document:

"It was accompanied by high tides and torrential rains in Louisiana. Port Arthur reported a wind velocity of 83 m.p.h. and a low barometric pressure of 28.87 inches. The hurricane produced tides of 4 feet at Port Eads; 6.4 feet at Frenier on the southwest shore of Lake Pontchartrain; 3.8 feet at Grand Isle; 4 to 5 feet near the mouth of Vermilion River; 5.6 feet at Schooner Bayou Control Structure, 16 miles south-southwest of Abbeville; 4.8 feet at Calcasieu Pass in the vicinity of Cameron; and 4.3 feet near Sabine."

Apparently, prolonged east winds piled up more than 6 feet of storm tide on the west end of Lake Pontchartrain in 1940. It is likely that water levels were also elevated near the Lake Borgne/ Shell Beach area, as well as along the levee of the Mississippi River, south of New Orleans. Storm tide values along the south Louisiana Coast generally ranged from 3.8 to 5.6 feet.

Now back to Debby. East and northeast winds along coastal Louisiana are already elevating water levels. Storm surge values at Shell Beach, LA were already approaching 2.5 feet this morning, according to NOAA Tides and Currents. I do not have a read on water levels at Frenier, although I may make a trip down there today or tomorrow to see for myself.

Once again, it should be stressed that the models remain uncertain and we should not just look at one possible scenario. All interests along the U.S. Gulf Coast, from Texas to Florida, should stay tuned to the National Hurricane Center, your local National Weather Service forecast office, and local media outlets for updates on this developing storm.

Check back often to this blog for the latest surge observations and historical comparisons. I will update the blog every morning and evening while Debby is in the Gulf of Mexico.

Saturday, June 23, 2012

Tropical Storm Debby forms in the Gulf of Mexico

National Hurricane Center best track forecast as of 7PM CDT, Sat Jun 23, 2012

Hurricane Bonnie (1986) tracking map, provided by Unisys Corporation. Green = tropical depression, yellow = tropical storm, red = hurricane

Tropical Storm #1 (1941) tracking map, provided by Unisys Corporation. Green = tropical depression, yellow = tropical storm, red = hurricane

Tropical Storm Debby formed this afternoon in the Gulf of Mexico. This is an interesting storm, as the models have predicted a wide range of possible outcomes. In general, the GFS model has insisted on a more eastward track, while other models have arrived at a solution that brings Bonnie on a more westward track. Most models seem to indicate that Debby will drift to the north or northwest in the near future.

The National Hurricane Center has leaned toward the westward track, taking Debby on a slow progression south of Louisiana, toward the Texas Coast. However, it's important to understand that with such low model consensus, anything is really possible.

This blog looks at historical hurricanes and tropical storms that resemble active storms to try to gain context about storm surge potential. We pull our surge data from SURGEDAT, the world's largest archive of historical storm surge data. SURGEDAT now has peak surge data for more than 500 surge events around the world, including more than 200 for the U.S. Gulf Coast. We have also built entire inundation envelopes for most storms, giving us a total of more than 4,600 high water observations for the U.S. Gulf and Atlantic Coasts.

As the forecast for Debby's track and intensity is quite uncertain, I just looked up historic tropical storms that tracked from east to west, with slow forward motion, south of the Louisiana Coast. Such a track is possible Monday into Tuesday, according to the NHC forecast. I'm not looking into surge history for the Central Texas Coast yet, as much uncertainty exists and Texas impacts would come later. The best two historical comparisons I could find related to westward-moving, slow tropical storms south of Louisiana were...drumroll please....

Hurricane Bonnie in 1986 AND Tropical Storm #1 in 1941

Hurricane Bonnie 1986
Tracking and Max Winds: This storm slowly moved to the west as a tropical storm while S of the LA Coast, then became a hurricane while still S of LA. Then storm tracked to NW, and produced max winds of around 86 MPH before making landfall in SE Texas

Storm surge observations:
Peak Surge: 5.2 feet at Sabine Pass, TX
Additional Surge Obs:
3-4 feet at Bolivar Peninsula, TX
2.7 feet above Mean Sea Level (MSL) at Paris Road, LA
2.4 feet above MSL at Bayou Bienvenue, LA
2-3 feet at Calcasieu Pass
2.2 feet at Galveston Island
1.7 feet above MSL at Rigolets, LA
1.6 feet above MSL at Industrial Canal, LA
Source of obs:

Tropical Storm #1 in 1941
Tracking and Max Winds: This storm developed into a tropical storm and tracked slowly to the W, staying S of the LA coast. It eventually turned toward NW and made landfall in SE TX as a minimal tropical storm. Max winds only reached 46 MPH.

Storm surge observations:
Peak Surge: Approximately 3.25 feet at Sabine Pass, TX.

"…the storm center passed about 50 miles south of Burrwood, and moved inland west of Port Arthur on the 14th. Tides slightly over 3 feet were reported along the coast and very little damage occurred." 

Source of obs: (U.S. Army Corps Report, titled, History of Hurricane Occurrences along Coastal Louisiana, pg 30.)

A few thoughts:
Again, the track and intensity for Debby are still up in the air. However, based on the best track and intensity provided by the NHC, I've pulled surge data for two storms that tracked slowly from east to west, staying south of the LA coast, Bonnie (1986) and TS #1 (1941).  Both turned to the NW and made landfall in SE TX. Bonnie became a minimal hurricane, while TS #1 barely maintained TS status. Based upon the current forecast, it may seem reasonable that Debby tracks west with an intensity somewhere in between those two storms. The peak surges for both events were observed at Sabine Pass, TX; Bonnie's surge was 5.2 feet and TS #1's peak surge was 3.25 feet.

While these events may provide some context for Debby's surge, please keep in mind that every event is different and surge heights can be very localized. Debby is forecast to move very slowly in the near future before making the turn to the west, and this pattern should enable prolonged E winds to impact SE LA. Generally, prolonged E winds in this area pile up water on the east side of the MS River delta, from near Venice, north to the Lake Borgne/ Shell Beach area, as well as Lake Pontchartrain, the Rigolets, and even the Mississippi Sound. Surge levels this afternoon and evening already approached two feet above normal at Shell Beach, according to NOAA Tides and Currents.

Stay tuned to this blog over the coming days. I will provide updates every morning and evening, as well as possibly some actual footage (pics and maybe video) from southeast LA and MS.

-Hurricane Hal