Unusual summer nor’easter brings heavy rain, gales and rough seas to the coastal Atlantic

An abnormally strong low pressure system impacted the Mid-Atlantic States over the weekend. During the time of year when attention usually turns to the tropics, a winter-like Nor’easter lashed areas from D.C. to Atlantic City. The storm was spawned by a broad 500mb Analysis valid 12z 29 July 2017deep-layer trough diving into the northeastern United States from Ontario. An extended area of surface low pressure formed on Friday morning. This low stretched from Boston southwestward through West Virginia before becoming organized over Virginia during the afternoon hours. Above average sea-surface temperatures allowed ample moisture to push across the Delmarva Peninsula toward the nation’s capital. Widespread heavy rain showers developed Friday afternoon and evening, and flash flood warnings were issued from D.C. to Baltimore. Before the storm wound down on Saturday, over four inches of rain had fallen across Maryland’s most populous city, with areas to the east seeing almost six inches of rainfall.

Conditions were no better offshore, where Gale Warnings were issued from Morehead City, North Carolina to Cape Cod, Massachusetts. As the system was developing, model guidance indicated the potential for wind gusts near 70mph offshore, which is near hurricane force. Fortunately, these extreme winds did not materialize, but widespread sustained winds in excess of 35mph were noted from the Chesapeake Bay northeastward toward Rhode Island. This allowed seas to become quite rough, with significant heights pushing 12 feet just off the coast of Delaware Saturday evening.

The unseasonable strong storm finally subsided on Sunday while quickly moving east of the region. Although not tropical in nature, this weekend’s system was a reminder that the East Coast is entering the time of year where weather becomes the forefront of the mind, and this could be even more the case this August, as it looks to be particularly active in the tropics. Stay tuned!

From record heat to monsoon thunderstorms within a week

One of the most anticipated seasonal weather changes during the northern hemisphere summer is the North American Monsoon. This monsoonal circulation produces significant rainfall over western Mexico and the Southwestern United States in response to summer heating over the higher terrain. While the monsoon brings beneficial rain, it can produce hazardous conditions over the desert. Monsoon thunderstorms may produce frequent lightning, hail, powerful flash floods, and blowing dust.

500mb Height Forecast NAM_Pivotal Weather
500mb Winds, NAM 18hr forecast valid 18Z  July 16, 2017

The onset of the monsoon is strongly influenced by the positioning of a 500mb area of high pressure. When this high is positioned over the Four Corners region, winds at this level turn more easterly over Arizona. Easterly flow allows inverted troughs to move west across the area, providing greater instability for thunderstorm development. Of greater significance is the resulting deep moisture advection from the Gulf of California. In July, mid-level winds over the Gulf of California are south to southeasterly, rounding seasonal high pressure that extends westward across the Gulf of Mexico during summer. Surface winds over the same region are southerly, transporting significant low-level moisture from both the eastern Pacific and Gulf of California. Lower wind speeds and weaker high and low pressure circulations are expected during summer as a result of less temperature variations. This often creates slow-moving monsoon thunderstorms, bringing an elevated risk of flash flooding.

Surface Moisture and Winds GFS_Pivotal Weather.png
Surface Dew Point & 10m Wind, GFS 6hr forecast valid 06Z July 17, 2017

Sunday, July 16th was the first very active day of the 2017 American monsoon season with nearly ideal conditions for hazardous weather over Arizona. With monsoon moisture on the rise, a Flash Flood Watch was issued for south central Arizona, including Phoenix. The forecast called for numerous thunderstorms over the higher terrain, propagating west to southwest across the lower elevations through the evening hours. NWS Storm Prediction Center issued a mesoscale discussion that afternoon detailing the threat of severe winds. Prime ingredients downstream included 20-25 knot easterly mid-level flow and sufficient instability as most unstable CAPE approached 2000 J/kg. Several severe thunderstorm warnings were issued by the National Weather Service forecast office in Phoenix that evening. At 6:16pm, a blowing dust advisory was issued for Northwestern Pinal County into southern Maricopa County until 8pm.

Severe thunderstorm warnings continued through the evening and early overnight hours. Flash Flood Warnings were issued for 30 minute rainfall totals exceeding 0.5 inch north and west of Scottsdale, according to the Flood Control District of Maricopa County (FCDMC). It is common for lower elevation areas and valleys to experience their heaviest rains at night.NWS Phoenix Tweet 16 July 2017

According to NWS Phoenix, this activity brought temperatures down to 74°F, which was the first time the area had experienced 70° temperatures in nearly 30 days. It is typical of the monsoon to onset quickly, causing an abrupt change in weather conditions. Earlier this month, the Phoenix area was setting record high temperatures of 118-119°F.

Here are some strong wind reports from the storms this day:

16 July 2017 Wind Reports Table Arizona
More wind reports can be found here.

What is the Madden Julian Oscillation (MJO)?

The Madden Julian Oscillation (MJO) is an intraseasonal fluctuation that primarily initiates over the warm waters of the Indian Ocean and western Pacific.  The MJO is comprised of regions with various atmospheric features such as deep convection and atmospheric wind anomalies that propagate eastward along the ITCZ. During a convective phase of the MJO, there is an enhanced region of tropical convection and moisture resulting in above-average rainfall. The opposite is true for a suppressed convective phase. As the MJO continues propagating eastward, the monsoon trough weakens and may shift southward. East of the MJO the easterlies are strengthened, and to the west, the easterlies are weakened. Therefore the passing of positive phase MJO can affect atmospheric wind shear, which could in turn affect tropical cyclone activity.

Phillip Klotzbach studied the relationship between the MJO and the development of tropical systems in the Atlantic Basin. In his 2010 study, Klotzbach found a direct relationship between the increase in vertical wind shear and relative humidity, and enhanced tropical cyclone activity and intensification. In the convectively enhanced phase of the MJO, upper-level easterly and low-level westerly wind anomalies act together to reduce vertical wind shear. One primary ingredient for tropical cyclone development is reduced vertical wind shear. Relative humidity throughout the atmosphere is also needed for tropical development. In Camargo’s study (2009), he found that mid-level relative humidity played the most important role, compared to low-level absolute vorticity, vertical wind shear, and potential intensity in tropical cyclogenesis by the MJO. Therefore, when an eastward moving MJO and a tropical wave meet, it is possible for the tropical wave to develop into a tropical cyclone due to the enhanced atmospheric moisture and reduced vertical wind shear created by the MJO.  If a tropical cyclone already exists, its interaction with a MJO may cause the cyclone to intensify. Kingtse C. Mo discusses an increase in tropical cyclone activity over the Atlantic Basin when the convective phase of the MJO is located the Indian Ocean rather than the Pacific Ocean.July9

 

The image above represents a forecast for Outgoing Longwave Radiation (OLR) anomalies, a key detector for active MJO regions, issued by NOAA’s Climate Prediction Center (CPC). The CPC monitors and predicts climate variability and teleconnections for government, public, and private meteorological industries. Negative OLR values indicate enhanced convection or an active MJO phase (more cloud cover indicating more convective activity). Positive OLR values represent suppressed convection (less cloud cover).

The latest forecast from the ensemble mean GFS predicts an increase in OLR, possible MJO wave, across the Indian Ocean for the next two weeks. As Kingste C. Mo found in his study, there is likely an increase in tropical activity over the Atlantic Ocean when an MJO is present over the Indian Ocean.

Although Wilkens Weather is forecasting a very low chance for tropical development in the next five days, this will be a parameter worth watching this tropical season.

Why we treat some Invest areas like tropical storms…

It’s critical that offshore operators are aware of tropical hazards well in advance of tropical storm development. 

Tropical Storm Bill, June 16 2015
Infrared Satellite of Tropical Storm Bill approaching the Texas coast.

Two years ago we were monitoring an area of disturbed weather near the Yucatan Peninsula. At the time, forecast models indicated that a trough of low pressure would move offshore the Yucatan within the next 24 hours and form a closed circulation as it tracked northwest toward the Texas coastal bend. Hurricane Carlos, off the southern coast of Mexico, was feeding in abundant tropical moisture from the Pacific, aiding thunderstorm development. Over the next few days, upper-level winds over the Gulf weakened, enhancing convection and improving the low-level circulation. Within 36 hours a tropical storm was designated over the northern Gulf of Mexico. About 15 hours later, Tropical Storm Bill made landfall over Matagorda Island, Texas with maximum sustained winds near 60 mph.Read More »

Summer Shamal winds and dust begin to impact the Middle East

As we transition to summer, our meteorologists prepare to forecast longer duration Shamal events. Shamal winds are strong winds that blow from the north to northwest over the arid Middle East. In winter, Shamals are associated with the passage of cold fronts. Cold fronts still influence the region’s weather through May, but by summer the region warms significantly and fronts become less frequent. Shamals from fall through spring are typically short-lived, lasting one to two days. By June, nearly stationary thermal lows along the monsoon trough over Northwest India, Pakistan and Southeast Iran interact with high pressure over the eastern Mediterranean and Saudi Arabia to produce more persistent northwesterly winds over the Arabian/Persian Gulf. Winds strengthen between these seasonal highs and lows as the low pressure areas intensify during summer months. Rao et al. (2003) found that gale force winds and rough seas offshore Qatar are more common in June than May and July. 

Shamal winds are strongest during the afternoon when hot surface air rises, creating turbulent eddies that mix winds higher in the atmosphere to the surface. High temperatures, strong winds and the seasonal lack of precipitation all contribute to the formation of blowing dust during these events. Sand and dust may be carried hundreds of kilometers across the Gulf states in dust storms, producing areas of near zero visibility. Read More »

2015 Holiday Storm Retrospective

A powerful storm system tracked across the northern Great Plains this holiday season. Heavy snows and blizzard conditions were observed in the Dakotas, strong storms occurred in Kansas and Missouri, and an ice storm developed in areas between. Of significant note was a tornado report in Kansas that if confirmed would be the first tornado recorded on Christmas day in that state. In addition, wind gusts in excess of 70 mph were reportedIowa Environmental Mesonet Wind Speed Reports December 2016 in northwestern Iowa, causing structural damage in the area. These conditions are a stark reminder that like meteorologists, Mother Nature does not take the holidays off. Interestingly, a similar storm system impacted the southern plains last holiday season.

One year ago, a major storm system moved from Texas through the Great Lakes, capping off a year filled with extreme weather in Texas and beyond. Read More »

On The Road: Aaron Studwell at AGU

This week, our Manager of Weather Operations, Aaron Studwell, is attending the 49th Fall Meeting of the American Geophysical Union (AGU) in San Francisco, CA.  While the core purpose of this trip is associated with Ph.D. work in Atmospheric Sciences at the University of Houston, Aaron is also attending sessions ranging from the initiation of lightning in developing thunderstorms to the seasonal forecasting of winter storms across the North Atlantic Ocean to the analytic theory of wind-driven seas.

Harmattan Dust in West Africa

As we approach the end of the calendar year, meteorologists, once again, encounter a significant weather phenomena that can sometimes be a challenge to forecast: The Harmattan Winds.

Harmattan winds are derived from a dry and dusty, northeasterly trade wind that originates in the Sahara. As the monsoon trough shifts south during the boreal winter, the trade winds will travel further south reaching the West Coast of Africa. This type of wind is strengthened by low pressure over the north coast of Guinea and high pressure over Northwest African Journal of Environmental Science and Technology Harmattan DustAfrica. The Harmattans can carry desert dust into the Atlantic and the Gulf of Guinea leading to hazardous operations on and offshore. Another element to the strength of the Harmattan is eastward movement of a low pressure system over Europe and its subsequent surface cold front that will move over the Mediterranean into North Africa. While the cold air will mix and warm over Africa, the wind will continue to surge south carrying with it the blinding dust covering everything in its path. Crop soil from the Sahel, the region between the Sahara desert and humid savannas, can also be mixed up in the winds further dropping visibility.Read More »

Major Hurricane Wilma, 11 years later

CIMSS NOAA Satellite Montage WilmaHurricane Wilma was the 21st named storm of the infamous 2005 Atlantic hurricane season. From her formation on October 15th to her demise on the 26th, Wilma would become one of the most memorable hurricanes in Atlantic basin history. As the 4th category 5 hurricane of the year, Wilma would become a monstrous bookend to an incredible, record-setting season.Read More »

Remembering 2005’s Major Hurricane Rita in the Gulf of Mexico

Hurricane Rita made landfall in extreme southwestern Louisiana on September 24th, 2005 with an intensity of 100 knots (Category 3). About 48 hours earlier, Rita was a Category 5 hurricane with a minimum pressure of 895mb, the fourth-lowest central pressure on record in the Atlantic basin. Although Rita’s history was overshadowed by Katrina, which made landfall just a few weeks earlier, the storm provided a unique challenge for both forecasters and public officials.

NASA Rita Terra satellite_20050918
NASA satellite image of Tropical Depression Eighteen over the Bahamas on Sept. 18, 2005

Rita originated as a weak tropical wave off the western coast of Africa on September 7th. The Saharan Air Layer, commonly known as Saharan Dust, and high levels of wind shear prevented the wave from producing thunderstorm activity as it moved across the tropical Atlantic. Conditions became more favorable for development later in the month as the wave reached the Bahamas. A tropical depression formed on September 17th and the system was designated as Tropical Storm Rita the following afternoon.

Rita continued to strengthen as it tracked across the Florida Straits, reaching Category 2 status by the time it reached the Gulf of Mexico on the 20th. Over the next 18 hours, the storm underwent rapid intensification over the Loop Current, becoming a Category 5 storm with an intensity of 145 knots. Rita continued to intensify and recorded an incredible 70mb drop in central pressure in a 24-hour period. At maximum intensity on September 22nd, Rita’s central pressure was estimated to be 895mb with winds near 155 knots (178 mph).

NASA Aqua satellite_20050923
NASA satellite image showing Hurricane Rita approaching the Gulf coast on Sept. 23, 2005

Thankfully for the residents of the Gulf Coast, Rita did not maintain its unprecedented strength as it pushed ashore. After moving past the Loop Current the system gradually weakened to a Category 3 before making landfall near Sabine Pass as a major hurricane. Hurricane force winds spread over 150 miles from the center while tropical storm force winds stretched as far north as the Louisiana/Arkansas border. Peak storm surge of nearly 17 feet occurred on the eastern side of Rita, causing severe flooding in several parishes in southwestern Louisiana. Heavy rainfall worsened this situation, with most of southwestern Louisiana receiving 7-10 inches, with some areas receiving over 15.

Rita continued to progress northeastward after being absorbed by a front across the central United States. That accelerated movement prevented a significant flood event in the Ohio River valley, with most rainfall totals being limited to around 2-3 inches as the remnant low raced toward the Great Lakes.

Although meteorological impacts to extreme southeastern Texas and southwestern Louisiana were unforgettable, only seven direct deaths occurred as a result of Rita in the United States. Most citizens in the southwestern Louisiana coastal areas evacuated before the worst impacts arrived, likely significantly reducing the death toll in that area.

The majority of the storm’s causalities occurred during the evacuation iWWT Hurricane Rita Wind Speed Analysisn Texas, where poor planning and heightened fears, resulting from Katrina, resulted in mass gridlock around Houston. Over 100 Texans perished due to accidents, fires, and health related issues during the evacuation. Much work has since been done to streamline the evacuation process from the Houston area, including the streamlining of the contraflow process on major highways exiting the city.

 

 

Remembering 2008’s Hurricane Ike

Hurricane Ike produced devastating storm surge as it came ashore over the east end of Galveston Island on September 13th, 2008.

Formation & Impacts to the Caribbean

Ike originated as a tropical wave off the coast of Africa and moved west-northwest across the Atlantic. The National Hurricane Center (NHC) designated the system as a tropical depression on SepteNHC forecast track for Hurricane Ikember 1st. The storm became significantly better organized by the 3rd and was upgraded to a hurricane that afternoon. Early the next morning, Hurricane Ike reached major hurricane status (Category 4) with maximum sustained winds of 125 knots and an estimated central pressure of 935mbThe storm weakened over the next few days due to moderate wind shear from high pressure to the northwest. This high, over the western Atlantic, was strong enough to force an unusual turn to the west-southwest. This heightened the threat for the Bahamas and northwestern Caribbean. 

This uncharacteristic turn led Ike into a more favorable environment, causing the storm to re-intensify to Category 4 status. The cyclone made its first landfall on Great Inagua Island in the southeastern Bahamas the morning of September 7th. 5-7 inches of rain were reported on the island and high winds destroyed several structures including a cruise ship terminal.  The economic impacts for Turks and Caicos and the Bahamas was estimated between $50 and $200 million (USD). Additionally, Ike’s rainbands caused deadly flooding and mudslides in Haiti – a country still recovering from three tropical systems that hit earlier that year (Fay, Gustav, and Hanna).

Hurricane Ike continued tracking west and made its second landfall near Cabo Lucrecia, Cuba on the morning of September 8th. Winds were estimated to be 115 knots (Category 4 status) at landfall. Large waves, as high as 50 ft, were likely responsible for damaged coastal homes and structures in the city of Baracoa. As much as 12-14 inches of rain fell on parts of the island.  Additionally, over 300,000 homes were damaged, 13% of which were total losses.  Destruction of crops, roadways and buildings also resulted in an estimated $3 and $4 billion (USD) in damages.  

Gulf of Mexico & Early Impacts to the Oil & Gas Industry

The mountainous island weakened Ike to a Category 1 hurricane as it passed briefly over the waters south of Cuba and entered the Gulf of Mexico near San Cristóbal, Cuba on the evening of September 9th.  Since Ike had weakened and lacked a tight inner core, high nasa_trmmsatwinds and heavy rains spread over an unusually large area as the storm tracked northwest across the Gulf of Mexico: Tropical storm and hurricane force winds extended 240nm and 100nm, respectively, from the center. The Tropical Rainfall Measuring Mission (TRMM) satellite passed over Ike early on the 12th, showing rainfall rates in excess of two inches per hour in the southeast quadrant of the storm.

Early preparations for Hurricane Ike caused at least 14 oil refineries in Texas and Louisiana to be shut down in advance of the storm, according to the U.S. Department of Energy. This was significant since over 1.3 million barrels per day of crude oil and over 7.3 billion cubic feet per day of natural gas could not be delivered to these facilities.

Landfall over Galveston Island, TX & Impacts to the United States & Canada

Ike maintained a large wind field over the central Gulf of Mexico as it tracked west-northwest toward the upper Texas coast through September 12th. In the hours before landfall, high water levels began impacting the Gulf coast as Ike turned north-northwest and strengthened to a Category 2 hurricane. Ike would make its third landfall along the northeast end of Galveston Island, TX early  on September 13th with maximum sustained winds near 95 knots (110 mph).

 

Ike Storm Surge Galveston Harris County Flood Control District

West of Grand Isle, Louisiana storm surge heights increased significantly: 10-13 feet from the southwest Louisiana coast to Port Arthur, Texas. The maximum storm surge recorded by any NOS tide gauge was 12.79 feet at Sabine Pass North, Texas. However, many USGS sensors indicated that there were likely localized areas with surge heights up to 17 feet. The Bolivar Peninsula and portions of Chambers County, Texas were most severely impacted by Ike’s storm surge. Most of this area was inundated by 10 feet of water. Widespread 5-7 inches of rain were reported across southeast Texas, with the highest amount measured north of Houston at 18.90 inches.  

NOAA Hurricane Ike Radar Loop

Tornadoes touched down in Texas (1), Louisiana (17), and Arkansas (9).  All of these were either EF0 or EF1 rating, which is typical within tropical air masses.  Storm-related fatalities totalled 19 in Texas, one in Louisiana, and one in Arkansas.  Damages across the three states totalled about $29.52 billion dollars, making it the second costliest hurricane to impact the United States, after Hurricane Katrina in 2005.

Although Ike weakened inland, the storm merged with a cold front on the 14th, which resulted in hurricane force wind gusts and 3-5 inches of rain across the Ohio Valley, an area just flooded by a passing low pressure system the week before. Storm-related fatalities across Tennessee, Ohio, Indiana, Illinois, Missouri, Kentucky, Michigan and Pennsylvania totalled 28.  Damage estimates for these states were nearly $4.7 billion. Hurricane force wind gusts and record rainfall were also reported across portions of southeastern Canada in the subsequent days.  

Weather Forecasting in the Adriatic

WWT Adriatic Sea WaterspoutHigh terrain extending across Italy and central Europe yield a challenging environment for weather forecasting in the northern Adriatic Sea, especially during the winter months. The Alps, 120 miles wide with several peaks over 15,000 ft, block colder air to the north and often deflect it to the east over the Balkan States. The cooler air accumulates over the Balkan Peninsula, eventually reaching the height of the mountain passes. This induces a Bora, a local downslope wind effect that is common and at times violent during the cold season, usually from October through March. The Bora is one of two local winds that impact marine customers in this region. The other being Sirocco winds, a strong southeast wind, which often build over the course of a couple of days ahead of a Bora or impending low pressure system and is usually forecast with less uncertainty.Read More »