15 June 2015
There is growing concern that a tropical cyclone may be forming in the Gulf tonight, and it will likely impact the Texas coast by late Monday. This system will probably not have time to reach hurricane strength but it does not matter since the threat is heavy flooding rains. While it will probably cross the coast well SW of Houston the heavy rains may affect the entire Texas coast, and with the very saturated ground near Houston and to the northwest into San Antonio and Austin, this is a serious threat.
Something to remember, is that wind kills few people in a tropical storm or hurricane. It’s storm surge on the coast and flooding rains inland, and if you don’t believe me, ask anyone from New Orleans. The Gulf of Mexico is very warm right now, warmer than usual in June, and this increases the threat of heavy flooding rains. So if you are in Texas, pay attention to the radar and don’t worry as much about the wind, or even where the center of the storm will make landfall. From satellite data this evening and model guidance, it looks like the wettest part of this system will be on the northern side, so a landfall on Padre Island could still cause floods in Houston and up to Austin. The warm oceans mean that where heavy rains fall, they can be exceptionally heavy.
One way of looking at potential rainfall is to look at what we meteorologists call precipitable water. When precipitable water starts approaching 50mm watch out!
I’ll leave you with a discussion from the NOAA Weather Prediction Center. This discussion is mainly for meteorologists but I think it is spot on, and covers a few things I did not mention above about model guidance.
QPF- precip amounts
GFS= US Longer range numerical model
ECM- European longer range model
CMC- Canadian model.
TPW- total precipitable Water.
QUANTITATIVE PRECIPITATION FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 603 PM EDT SUN JUN 14 2015
...WESTERN GULF STATES.... MAIN FOCUS IN THIS REGION WILL BE THE TROPICAL PLUME OF MOISTURE MOVING NORTHEAST ASSOCIATED WITH THE POTENTIAL GULF TROPICAL SYSTEM. REGARDLESS OF WHAT HAPPENS WITH THIS POTENTIAL TROPICAL SYSTEM...THERE SHOULD EB A HEAVY RAIN THREAT ACROSS PORTIONS OF SOUTHEAST TEXAS AS ALL THIS MOISTURE IS TRANSPORTED NORTH. MODEL DIFFERENCES FIRST EXIST WITH HOW QUICKLY CONVECTION DEVELOPS AHEAD OF THE SYSTEM MONDAY NIGHT. WPC BUMPED UP VALUES A BIT FROM THE PREVIOUS FORECAST...WITH THE ECMWF SEEMING ON THE DRY SIDE GIVEN THE EXPECTED MOISTURE AND INSTABILITY PRESENT ACROSS THE REGION. NEXT QUESTION IS WHERE DOES THE SYSTEM TRACK. PRETTY LARGE SPREAD AMONG THE GUIDANCE...WITH THE CMC A FAST OUTLIER...AND THE GFS MORE ON THE WEAKER AND WESTERN EDGE OF THE GLOBAL GUIDANCE. THUS WPC QPF FAVORED A SOLUTION MORE BETWEEN THE 0Z/12Z ECMWF...THE 12Z UKMET AND THE 12Z GFS ENSEMBLE PROBABILITIES FOR DAY 2. BY DAY 3 THE GFS ENSEMBLES BECOMES LESS USEFUL AND THE FORECAST WAS CLOSER TO THE ECMWF/UKMET CONSENSUS. THESE TWO HAVE BEEN PRETTY CONSISTENT WITH THEIR TRACK AND QPF AXIS...AND ARE PRETTY SIMILAR. THIS CONSENSUS ALSO CLOSELY MATCHES THE PREVIOUS WPC QPF FORECAST. THE ECMWF CONTINUES TO BE THE SLOWEST OF THE GUIDANCE...THUS USING THE UKMET IN THE CONSENSUS HELPED SPEED THE SYSTEM UP SOME. IT SHOULD BE NOTED THAT EVEN THOUGH CONFIDENCE ON AN AREA OF HEAVY RAIN IS HIGH...GIVEN THE SPREAD...THE EXACT LOCATION AND TIMING IS A LOW CONFIDENCE FORECAST.