Patricia And The Floods

20151023_VIIRS_I-Band5_Patricia20E_0523EDT

Hurricane Patricia underwent explosive intensification from a Category 1 to Category 5 hurricane in 24 hours. It went from 980 millibars to 879 millibars! That is the most rapid intensifying hurricane in the Western Hemisphere! To make matters worse, it has 200 mph wind! That is much stronger than Atlantic’s most intense hurricane, Wilma in 2005. To put that in perspective, Wilma peaked at 882 millibars. Patricia is about to barrel towards Mexico as a full blown Category 5 monster.

However, with any intense hurricanes, they tend to fluctuate in strength due to eyewall replacement cycle and wind shear. By the time Patricia makes landfall on Mexico, it has a central pressure of 920 millibars and 165 mph winds. On land that would be 141 mph due to a 15 percent reduction from friction. However, the friction increases the gust by a factor of 1.5, which would be 210 mph! A weather station in Chamela-Cuixmala Biosphere Reserve recorded 185 mph winds with gusts as high as 211 mph, which suggests the station got damaged. 185 mph sustained winds on land is 278 mph! That would be a nightmare anywhere! Think of that in a major city like Houston, New Orleans, Miami, or New York. It turns out that Patricia made landfall on Cuixmala, Jalisco, Mexico, which is between Manzanillo and Puerto Vallarta. Mostly small villages and towns were affected by Patricia’s strong winds. Also, people evacuated from the coast as storm surge is possible. The death toll at this writing is 13. Pretty low for a potentially catastrophic hurricane.

Patricia was an average sized hurricane. East Pacific hurricanes tend to be smaller than Atlantic hurricanes due to a smaller basin area compared to the Atlantic. At peak and landfall, hurricane force winds were 50 miles in diameter. In comparison, Hurricane Ike before it hit Southeast Texas had hurricane force winds of over 200 miles in diameter! Smaller sized hurricanes produce smaller storm surge. Larger sized hurricanes produce larger storm surge. One reason why Ike and Sandy were so bad despite not being strong like Patricia was their large size. Interesting to note that Katrina made landfall on the Mississippi Delta as a Category 3 hurricane with central pressure of 920 millibars. The reason for that is Katrina is a large hurricane like Ike.

So, what allowed Patricia to undergo explosive intensification?

It had large area of warm water. This is due to a strong El Nino and warm Pacific Decadal Oscillation (PDO).

20151022-23_SSTAnomaly_NA

There was a large area of Precipitable Water (PW) over the Pacific near Mexico. The values are easily over 2 inches.

20151022-23_850mb_PrecipitableWater_NA

The relative humidity was very humid. This is relative humidity at 10,000 feet or 700 millibar level. That is more favorable for tropical development. Dry air kills tropical development.

20151022-23_700mb_RelativeHumidityAnomaly_NA

As all strong hurricanes, they must weaken and in this case, the Sierra Madre Occidental sheared it apart. Mountains are deadly for hurricanes as they can cut through their circulation. Yet, mountainous areas see higher winds and heavier rain, especially on the windward side. Once Patricia is reduced to a tropical low, the moisture from it dumps heavy rain over Texas. The heavy rain affects a large area of Texas. The heavy rain is from a slow moving Pacific front and Gulf of Mexico and Pacific moisture.

North Texas sees some of the heaviest rain. Corsicana, Texas go hammered with the heaviest rain. Powell saw over 20 inches of rain in 24 hours! Southeast Texas saw widespread heavy rain with flooding. Many areas saw 5 to 10 inches of rain. Some areas saw over 12 inches of rain.

20151026_7Day_Rainfall_Total

Here is a GIS map I created from AHPS and US Drought Monitor. Notice the heaviest rains is around Corsicana. In the 7 days, many areas saw over 8 inches of rain with totals as high as 15 inches of rain. The rains are beneficial as Texas is in a severe drought. Corsicana and Dallas/Fort Worth Metroplex were in the severe drought. I expect they will be out of the drought by this week according to US Drought Monitor.

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