Tropical Storm Franklin For 8/9/2017 1900 CDT

The first hurricane of the season, Franklin, is getting ever closer to Mexico. It looks to be that way.

Franklin is a Category 1 hurricane with 75 mph 120 km/h 65 knots wind. It has gusts of 94 mph 150.4 km/h 82 knots. Further intensification is possible as shown in the forecast model. Two models keep Franklin as a hurricane despite being over the mountains of Mexico. I am not convinced that will happen as the mountains tend to weaken hurricanes.

I would not be surprised if Franklin becomes a Category 2 hurricane with 105 mph 168 km/h 90 knots wind right before landfall as looks to be intensifying further. Franklin is an average sized hurricane. Tropical storm force winds extend up to 140 miles 224 km/h 122 nautical miles. Hurricane force winds extend up to 35 miles 56 km/h 30 nautical miles. from the eye.

Most areas in Mexico will see at most tropical storm force winds with hurricane force winds. Hurricane force winds should be most likely confined to the coast. Here is a probability map of hurricane force winds.

If Franklin makes landfall as a 85 mph 136 km/h 74 knots hurricane, the strongest wind possible is 72 mph 115 km/h 63 knots with gusts as high as 108 mph 173 km/h 94 knots. I determine this by multiplying the strongest winds by 0.85. Land reduces wind by 15 percent. However, due to friction, gusts are higher as I multiply sustained winds by 1.5.

My main concern is heavy rain from Franklin. Franklin is moving as 12 mph, which means it can dump about 8 inches (20.32 centimeters) of rain. Many areas are likely to see 4 to 10 inches (10.16 to 25.4 centimeters) of rain. Mountains areas could see as much as 20 inches (50.8 centimeters) of rain. This amount is certainly going to lead to flooding that can be deadly.

Patricia And The Floods

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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).

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

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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.

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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.

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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.