14 June 2015

Tropical disturbance entering Gulf, heavy rain headed for Texas

Back on June 4, I posted some model forecasts on Facebook that showed a disturbance coming together in the eastern Pacific on June 8, then crossing over the Isthmus of Tehuantepec/Yucatan area, then entering and developing in the western Gulf of Mexico on June 12-13, and finally, heading for Texas on June 14.  Well, as unbelievable as it sounds, that is playing out with near-perfect accuracy!  Such forecasts were made by both GFS and ECMWF global models.

Enhanced infrared satellite image from 7:30am EDT.  The approximate center of the disturbance is marked with a white X, with general forecast trajectories in white arrows. (NASA)
As of Sunday morning, the disturbance is over the Yucatan peninsula... there is a 1008mb surface Low embedded within it, but the cloud cover and thunderstorm activity extends over a much larger area.  It has a fairly high likelihood of organizing further once it's over the Gulf of Mexico, and an aircraft reconnaissance plane will investigate it later today to help decide if a tropical cyclone has indeed formed.

Since this is a relatively large and disorganized system, the exact center of it does not matter much, but it does gives an idea of where the envelope of disturbed weather will be.   No model, as of now, is forecasting anything beyond a mid-grade tropical storm (which only tells you about the wind speed... tropical storms can still be very dangerous, costly, and deadly because of the rain).

Track forecasts for 91L (pre-TD2 or pre-Bill?) from Sunday morning.  The first three models are global; the last three are regional, and all agree of a northwest track toward Texas, then recurving inland. (UAlbany)
 By far,the biggest threat from would could become TD2 or TS Bill is heavy rainfall and flooding in areas that will not take much to flood: Texas and Oklahoma.  This system could bring 6+" of rain to some of those areas, plus a plume of heavy rain along its longer-term trajectory (through the Ohio Valley and the northeast US).

Five-day forecast of accumulated rainfall totals, valid from Sunday morning through Friday morning. (NOAA/WPC)
Here is another view of a rainfall swath, from the 06Z run of the GFS model, and just over the south-central US...

Five-day forecast of accumulated rainfall from the 06Z GFS run, valid Sunday morning through Friday morning. (tropicaltidbits.com)
Stay tuned for further updates...

01 June 2015

It Only Takes One: The Mantra of Inactive Hurricane Seasons

Another post today to usher in the beginning of the 2015 Atlantic hurricane season!  This one is provided by my good friend and guest blogger, Michael Laca.  Michael is a Miami native, and has experienced many hurricanes, both in Miami and on his numerous storm chases over the years.  He is very knowledgeable on hurricanes and particularly hurricane history, and is the owner of the popular TROPMET.COM website that has been around for over 20 years.

His post today address the common phrase It only takes one, referring to the destructive potential of a single landfalling hurricane, regardless of an "active" or "inactive" season. 

Today marks the beginning of the 2015 Hurricane Season in the Atlantic Basin. With a significant 'El Nino' event currently developing, seasonal forecasts that have recently been released from both CSU and NOAA are suggesting that below-normal tropical cyclone activity can be expected this year. Combined with a nearly decade-long absence of any major hurricane landfalls in the United States, the perceived threat among many coastal residents has been waning.

Of course, as is often heard, 'It only takes one!' to make a season catastrophic, but hearing this has always made me wonder how many times that scenario has actually occurred. Looking back at all "inactive" Atlantic seasons (based on a total of eight, or less, "named" storms within a given season) from 1900-present, how many major hurricanes (maximum sustained winds >= 100kt/115mph) have impacted the U.S.?

As it turns out, it's probably more than you might have imagined. During this period, there were 16 seasons that met my "inactivity" criteria, which also produced a major hurricane impact(s) in the United States. In the map below, the tracks for the 17 major hurricanes (which resulted in a total of 21 separate major U.S. impacts) can be seen, along with their respective peak intensities (in knots), and associated intensity at the time of major impact/landfall. Across these specific 16 seasons, the average number of "named" storms per year was 5.8, well below the statistical average of 9.6. (Note: The statistical average is based on the period 1950-2000, excluding many of the "inactive" seasons on my list, which predate the modern reconnaissance and satellite eras. The statistical average is presented only as a general reference.)

 Some of the most notorious hurricane impacts, and greatest disasters, that this country has experienced have occurred within these "inactive" seasons, including the Galveston Hurricane of 1900, the Texas and Louisiana Hurricanes of 1915, the Okeechobee Hurricane of 1928, the Great Labor Day Hurricane of 1935, Hurricanes Audrey, Donna, Betsy, Beulah, Alicia and, of course, Hurricane Andrew. The combined number of fatalities from these specific storms is a staggering 17,100! Also, looking at the distribution of the U.S. locations impacted by these particular storms, 1 impact occurred in North Carolina, 4 occurred in Louisiana, 6 occurred in Texas, and a whopping 11 major hurricane impacts have occurred in Florida, during "inactive" seasons... 9 of those over the southern portion of the peninsula... and 5 within a 60 mile stretch south of Miami to the middle Florida Keys!

It's important to re-state that this list is strictly limited to impacts from tropical cyclones that were of 'major' hurricane intensity (Category Three, or higher, on the Saffir-Simpson Hurricane Wind Scale). There have been many other impacts in the United States, during "inactive" seasons, from hurricanes (and other storms), below Category Three intensity... some of which have produced devastating results (such as Hurricane Agnes in June, 1972)!

So, regardless of how many tropical cyclones develop in the Atlantic this year, please remember to always be prepared because it truly does ONLY TAKE ONE ... and there have actually been many "ONES" to prove it!

-- Michael Laca

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The 2015 Atlantic Hurricane Season Begins Today

My introduction to the 2015 Atlantic hurricane season can be found on the Washington Post's Capital Weather Gang blog at:

The 2015 hurricane season begins today