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Extreme Tropical Storm Precipitation

Hurricane Matthew: By The Numbers

By | Extreme Tropical Storm Precipitation | No Comments

It has been over 10 years since the east coast of the United States has seen a major (category 3 or higher) hurricane hit its shores. Not since Hurricane Wilma in 2005 has a hurricane with such intensity moved ashore in the United States. Hurricane Matthew, which formed near the northern coastline of South America, became a hurricane on September 29th, and spent the next week and a half slowly churning its way up through the Caribbean and through the southeastern US before moving off into the waters of the mid-Atlantic. Indeed, the “hurricane drought” that the eastern US seaboard has experienced over the last decade has been the longest on record. Before impacting the US, the shear destruction that Matthew caused in Haiti and eastern Cuba is hard to imagine. In Haiti, over 900 people dead, on top of famine and Cholera outbreaks, has shaken an already struggling country to its core.

Destroyed houses are seen after Hurricane Matthew hit Jeremie, Haiti, October 6, 2016. REUTERS/Carlos Garcia Rawlins     TPX IMAGES OF THE DAY      - RTSR4LP

Destroyed houses are seen after Hurricane Matthew hit Jeremie, Haiti, October 6, 2016. REUTERS/Carlos Garcia Rawlins TPX IMAGES OF THE DAY – RTSR4LP

With few rain gauge networks within Haiti and Cuba, it is difficult to estimate the total amount of rainfall that fell over these countries as Matthew tore through. However, it is estimated that between 20 and 40 inches of rain hit Haiti, on top of deadly storm surges and hurricane-force winds. Despite storm surge wave heights over 25 ft, no fatalities were reported along Cuba’s shoreline communities. Moving through Haiti, Cuba, and the Bahamas Matthew weakened somewhat to a category two hurricane until it moved back out into open waters and on its was to the US coastline. Rainfall estimates in the Caribbean, via the National Atmospheric and Oceanic Administration, are shown below:

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As Matthew neared Florida, it strengthened back into a category 3 (major) hurricane as it moved over a very warm sea surface. A massive complex of swirling thunderstorm bands, Matthew had both an inner and outer eye wall, stretching nearly 100 miles in diameter. The radar reflectively image below shows the shear size of Matthew as it brushed against the Florida coastline.

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Matthew continued to spin up the east coast over the next few days, gradually losing energy and weakening. Its snail-like pace, however, meant that coastal cities saw torrential rainfall for over a day. Total precipitation for Matthew, below, shows areas with 10+” of rainfall from just north of Jacksonville, FL up to southern Virginia. The heaviest rains hit areas just north of Savannah, GA and near Fayetteville, NC.

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MetStorm mass curve plots for both Georgia and North Carolina are plotted below. In these images, both incremental and accumulated precipitation over the 72 hour-duration of our MetStorm run of Hurricane Matthew are shown for the latitude/longitude point of highest precipitation: near Savannah, GA and Fayetteville, NC. Note the similarities between both of these mass curve plots, with roughly a full day of heavy precipitation as Matthew’s thunderstorm bands swept up north through the east coast.

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The final analysis we have performed with MetStorm is determining the average recurrence interval (ARI) for the 24 hours that the heaviest of rainfall fell in all areas of our analysis domain. The ARI is a measure of the “rarity” of a rainfall event, and so we can see that many areas received 24-hour rainfall totals that have a probability of occurring less than 1 in 500 years. Locations near the peak amount of rainfall, mentioned above, are over a one thousand-year rainfall event: exceptionally rare.

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This massive amount of rainfall, coupled with very wet antecedent conditions, has of course lead to extreme flooding, especially in the Carolinas, as overflowing rivers could not contain the amount of runoff they were receiving. With a US death toll now 46 and a cost of $1.5 billion in North Carolina alone, Matthew will go down as a deadly and very costly hurricane for the east coast. Take a look at the before and after areal photos of the flooding in the Carolinas below:

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Courtesy of The Weather Junkies.

This Hurricane season is proving to be a very active one. With a month and a half left in the North Atlantic Basin hurricane season, we’re hoping major storm activity veers away from the east coast.

Please note that the maps presented here are preliminary and will be updated when new data become available. If you are interested in this product, or any other product from our MetStorm Precipitation Analysis tool, please email us or send us a message though our contacts page here.

-MetStat Team


Floodwaters from Tropical Storm Bonnie

By | Extreme Tropical Storm Precipitation, MetStorm | No Comments

Bonnie faced a tough environment for organized storm formation as she crept towards the Carolina coasts, with strong southerly wind shear and dry coastal air constantly trying to rip the storm apart. By the time Bonnie made landfall she was, in fact, a tropical depression. This was no consultation for the people living and vacationing near the North and South Carolina coasts, however, in the midst of the busy Memorial Day weekend. Two deaths by drowning due to strong rip currents generated by Bonnie’s sustained >40 mph winds as well as over $600,000 in damages left a shadow over what should have been a relaxing long weekend. Below is the storm track for Bonnie, courtesy of the Plymouth State Weather Center, showing its landfall along the South Carolina Coast.

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The bands of convective storms swirling around the center of Bonnie created a large swath of heavy precipitation across the region just north of Savannah, GA and to the west of Charleston, SC. The maximum amount of precipitation that fell over the entire period in which Bonnie produced rainfall (here defined as the 72 hours from 7am May 28 – 7am May 31) was 11.84 inches. This rainfall was mostly concentrated over two areas, shown below: south of Statesboro and south and west of Hampton. Also plotted below is the MetStorm-generated precipitation mass curve plot at the area of largest recorded total rainfall, which was just north of Ridgeland, SC. The striking thing about this plot is the quick ramp-up of precipitation as Bonnie approached land, culminating in more than 2 inches per hour in the early morning of May 29th. Precipitation intensity here and throughout the area quickly fell off to a continued light rainfall for the next couple days as Bonnie turned and ventured out to sea once again.

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The average recurrence interval, or ARI, is widely used to convey the rareness of rainfall events. An ARI is the probability of the occurence of a recorded rainfall amount over a specified duration in a given year. Below, the 6-hour ARI value for rainfall is plotted over the Bonnie storm area. The largest value of 211.76 years, again near Ridgeland, therefore means that at this point the largest 6-hour rainfall total produced by Bonnie is expected to occur on average every 211.76 years. Many areas effected by Bonnie saw 6-hour ARIs of over 25 years: no small event.

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Flooding near Ridgeland caused the city’s wastewater treatment plant to overflow, dumping close to 100,000 gallons of wastewater into the nearby river system, and as with most storms, pictures from the public describe in detail extreme events in a more familiar manner than data can provide. Bonnie, along with Hurricane Alex before her, have signaled an early start to the Atlantic hurricane season.

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photo courtesy of twitter user @cookies4monster

Please note that the maps presented here are preliminary and will be updated when new data become available. If you are interested in this product, or any other product from our MetStorm Precipitation Analysis tool, please email us or send us a message though our contacts page here.

-MetStat Team


Hurricane Patricia remnants cause extreme rains in Texas and Louisiana

By | Extreme General Storm Precipitation, Extreme Tropical Storm Precipitation, MetStorm, Uncategorized | No Comments

Hurricane Patricia was a force to be reckoned with not only in its record breaking intensity by central pressure, but also by its impressive rainfall in the Gulf coast states. If the minimum pressure recorded by NOAA’s Hurricane Hunter aircraft of 879 hPa verifies, it will beat the Hurricane Wilma for the most intense tropical cyclone by central pressure in the Western Hemisphere. Another astonishing fact about Hurricane Patricia was its impressively quick transition from tropical storm to category 5 hurricane in 24-hours. Winds recorded on October 22nd at 3UTC (9pm MDT) were at 65mph, which classified it as a tropical storm. One day later on October 23rd at 3UTC (9pm MDT) winds had reached 160mph, classifying it as a category 5 Hurricane. In the same 24-hour period the central pressure had decreased from 994 hPa to 924 hPa, making an impressive 70 hPa drop in pressure.

As the system passed over the Sierra Madre mountains in Mexico, it weakened rapidly and dropped below the wind requirements for a tropical depression before it arrived on the east coast of Mexico. As the remnants continued east-northeast into the Gulf of Mexico, the warm moist air was advected over the Gulf coast states. This moisture fueled the large rainfall totals experienced in Texas and Louisiana over the weekend. In a preliminary MetStorm analysis from October 22nd at 12Z (6am MDT) through October 26th at 12Z (6am MDT) the maximum estimated precipitation was 22.5″ over the location south-southeast of Dallas, Texas. Other precipitation estimates for this storm near North Houston were around 10″ and around Baton Rouge were a little over 9″. The bulk of the precipitation, as shown by the mass curve plot below, at the storm center near south-southeast Dallas occurred in a short period of time, with showers trailing over the next day and a half.

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Please note that the maps presented here are preliminary and will be updated when new data become available.  If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at media@metstat.com or through our contacts page at here.

-MetStat Team




 

1000-year Rains in South Carolina, October 2015

By | Extreme General Storm Precipitation, Extreme Tropical Storm Precipitation, MetStorm, Uncategorized | No Comments

Here at MetStat, we are continuously monitoring the situation as Hurricane Joaquin continues on its path northward. As the impacts from the precipitation of this event unfold we will be regularly updating our blog, facebook, and twitter pages with the latest information available, so check back often. Our Quantitative Precipitation Forecast (QPF) product, initialized from the 15Z (11 EDT) Weather Research and Forecasting (WRF) model run, shows significant precipitation forecasted to impact South Carolina in a 24-hour period ending at 3Z (23 EDT) this Sunday, October 4th. Shown below following the QPF map, is the Extreme Precipitation Index map, which depicts the rarity of the forecasted 24-hour precipitation ending at 3Z (23 EDT) October 4th. If the current forecast verifies, this event will be extremely rare, with a return period at over 1000-years (in other words, this event has less than a 0.1% chance of occurring in any given year). A similar QPF map of ours was featured in Dr. Jeff Masters blog about this storm. Dr. Masters post has great commentary on the meteorology and mechanisms involved in the set up and forecast of Joaquin. For additional information, visit his blog post here.

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If you want to monitor the rarity of the latest 6- and 24-hour precipitation in real time, there are also live Extreme Precipitation Index analysis maps available here.

As precipitation intensifies in the Carolinas and along the east coast we will be initiating MetStorm runs, in near-real time, to keep a pulse on the amount and rarity of precipitation falling, so make sure to check back often.

Update 10/9/2015

MetStat, Inc. is proud to share the most comprehensive rainfall and frequency analysis of the October 1-5, 2015 storm that caused catastrophic flooding in South Carolina. As forecasted, an “atmospheric river” of deep tropical moisture emanating west from Hurricane Joaquin interacted with a frontal boundary and a strong upper-level low parked over the Southeast. This produced a NW-to-SE band of extremely heavy rain that stretched across much of central South Carolina and caused 1000+ year rains. MetStat’s analysis was conducted using MetStorm™, a new, state-of-the-science hydrometeorological tool for characterizing storm precipitation.  This analysis utilized dual-polarization radar mosaics from Weather Decision Technologies, satellite estimated rainfall from NOAA, 845 quality-controlled rain gauge measurements (hourly and daily) from Synoptic Data Corp and NOAA, and MetStorm’s innovative algorithms to produce high-resolution, 5-minute rainfall grids/maps.  Below is a preliminary 96-hour rainfall map and corresponding Average Recurrence Interval (ARI) map. The maximum measured 96-hour rainfall was 26.88 inches at CoCoRaHS gauge MOUNT PLEASANT 6.4 NE, SC, while the highest derived rainfall was 30.68 inches along the central coast of South Carolina, just northeast of Charleston. The 96-hour ARI based on the MetStorm™ results and official precipitation frequency data from NOAA, exceeded 1,000-years (0.1% chance of occurring in any given year) across large areas of South Carolina.

Please email us at info@metstat.com or through our contacts page at http://metstat.com/contact-us/ for more information and other analytics (e.g. Depth-Area-Duration (DAD) plots/tables) available for this storm analysis.

-MetStat Team