Hurricane (now Tropical Storm) Harvey’s journey started rather arduous, then it entered a very favorable environment and the rest is ongoing history. After making landfall as a Category 4 (130 mph) hurricane on Friday, Harvey has moved in a tight cyclonic loop and is now just about to re-enter the Gulf of Mexico. After unleashing stunning rainfall totals in the Houston metro, the most intense bands of thunderstorms have been drifting east toward Beaumont and southwest Louisiana this morning. The break in Houston is likely temporary as additional rain bands will develop today, while Harvey may attempt some mild re-intensification prior to a second landfall near the Sabine River.
In the meantime, the tropical storm has taken on a rather hybrid, comma-shape in the last 24 hours, so what are the chances of Harvey making a comeback before a second landfall? What may impede it? How much more rain will fall in the Houston to Lake Charles area?
GOES-16 Air Mass RGB showing the evolution of Hurricane Harvey valid from 0000 UTC 08/25/17 – 2357 UTC 08/27/17. *Preliminary, Non-Operational Data* (Click here to open in a new window)
The GOES-16 Air Mass RGB animation above shows Hurricane Harvey rapidly intensifying prior to landfall, then changing shape as the cyclone weakens over eastern Texas. Note how the environment changes around the cyclone as more oranges appear in the animation due to an upstream shortwave (upper-level disturbance) drifting south-southeast into western Texas. This shortwave introduces some dry air into the western and southern portions of the tropical cyclone leading to a re-orientation of the strongest thunderstorms to the eastern quadrant (responsible for the Houston flooding).
IASI Ozone Anomaly valid at 0302 UTC on 08/28/17. (Click here to open in a new window)
Will Harvey now transition to an extratropical cyclone or will it remain tropical? The answer may lie in the Infrared Atmospheric Sounding Interferometer (IASI) Ozone Anomaly product as it shows little in the way of anomalous ozone surrounding Harvey (Blue coloring indicates 125%+ of normal ozone, indicative of a stratospheric intrusion). The normal (white) to slight below normal (brown) shading would indicate that there is no tropopause fold nearby and the shortwave responsible for the drying on the western flank of Harvey may be more transient, rather then directly leading to a full baroclinic transition. This would suggest the possibility that Harvey could intensify once back over the Gulf of Mexico.
But. . .As NHC Hurricane Specialist Pasch stated in the 4 a.m. CDT update, “Significant strengthening is not anticipated, however, due to the system’s lack of an inner core and strong southwesterly shear associated with an upper-level trough over Texas.” This makes sense as the system would need to detach from the aforementioned shortwave, spend more time over water, and rebuild the inner core to significantly intensify. The main threat will continue to be the heavy rain and significant flooding.
WPC Mesoscale Precipitation Discussion valid at 0500 UTC 08/28/17. (Click here to open in a new window)
GOES-16 7.3um water vapor animation valid from 0000 UTC to 0600 UTC on 08/28/17. *Preliminary, Non-Operational Data* (Click here to open in a new window)
WPC Forecaster Otto mentioned the 7.3 µm water vapor imagery in the 0500 UTC Mesoscale Precipitation Discussion (MPD) that focused on the continuing heavy rain threat in southeast TX into southwest LA”:
“EXPERIMENTAL GOES 16 7.3 MICRON LOW LEVEL WATER VAPOR
IMAGERY SHOWED RELATIVELY DRIER AIR WRAPPING AROUND TROPICAL STORM
HARVEY TO THE SOUTH INTO THE HOUSTON METRO REGION AS OF 06Z. THE
DRYING IS REFLECTED WITH A MLCAPE GRADIENT NOTED IN THE SPC
MESOANALYSIS AND THE RAP. ON THE WRN EDGE OF THE INSTABILITY POOL
WAS A SOUTH TO NORTH BAND OF HEAVY RAIN WITH RAINFALL RATES OF 2-3
IN/HR OVER CHAMBERS COUNTY…JUST EAST OF GALVESTON BAY.
REFLECTIVITY FROM KHGX WAS RELATIVELY QUIET FOR COASTAL COUNTIES
ALONG AND WEST OF GALVESTON BAY WITH ONLY LIGHT SHOWERS APPEARING
DESPITE TOTAL PRECIPITABLE WATER VALUES OF 2.3 TO 2.5 INCHES AS OF
06Z.”
CIRA Total Precipitable Water (microwave) product showing the greater than 2.3″ PW values at 0600 UTC 08/28/17. (Click here to open in a new window)
By using this particular water vapor channel, the forecaster is able to analyze the low-level water vapor gradients to determine where the best convergence will occur. To further emphasize the amount of moisture available to the east of Tropical Storm Harvey, the CIRA Total Precipitable Water product shows the 2.3″-2.5″ PWs that Forecaster Otto referenced in the MPD streaming onshore from the western Gulf of Mexico.
These tools are proving to be valuable to forecasters as they continue to assess the current and future threats posed by Tropical Storm Harvey.
For additional blog posts on Harvey, please visit our Proving Ground partner’s blogs:
https://nasasport.wordpress.com/
http://cimss.ssec.wisc.edu/goes/blog/
Thanks for reading!
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