As Harvey Winds Down, Hurricane Irma Waiting in Wings

Hurricane Harvey has left major devastation in Texas, but there is another hurricane called Irma out in the Atlantic which could take aim at the United States within the next week or so.

Irma became a hurricane early on the 31^st August and by the evening it was upgraded to a major hurricane, which requires sustained winds greater than 110 miles (177 kilometres) per hour.

Given the early stages, weather models are not in total agreement over Irma’s likely path or potential power, but all hurricane-prone areas – from the Gulf of Mexico clear up the Eastern Seaboard – could be in its target.

Concerns are heightened for residents in coastal regions of the Southern and Eastern United States in the wake of Harvey, which dumped a record amount of rainfall for the continental United States over the Houston area within the past few days, leaving tens of thousands homeless.

The damage is so devastating that Texas could require as much as US$125 billion in aid from the US government, larger than the record US$110.2 billion aid package assembled in 2005 following Hurricane Katrina.

Recent runs of the US GFS model suggest Irma could gain significant strength and impact the Eastern Seaboard the weekend of the 9^th September. Whether that means a direct hit on the Carolinas or the Northeast, or just an offshore encounter is still uncertain.

The European midday on the 31^st August model shows some more alarming possibilities, with the hurricane gaining strength, clipping the southern end of Florida, and heading into the Gulf of Mexico – perhaps the worst-case scenario for those still reeling from Harvey.

Although the Atlantic hurricane season is near its peak and storms in close succession are common, the prospect of another hurricane is stomach-churning. In addition to the human impact, Harvey has sent shockwaves through the transportation, energy, and retail industries, causing supply shortages and billions in losses.

Commodity Markets Jolted

With Houston at the heart of the US oil and gas industry, Harvey’s hit has been felt most directly in the energy markets. The catastrophic flooding has shut down nearly a quarter of US oil-refining capacity, threatening a national supply crunch.

As such, benchmark US gasoline prices hit two-year highs on the 28^th August and tested nearly three-year highs on the 31^st August, and gasoline margins have rallied to the strongest levels in five years for this time of year.

Transportation woes are plaguing the agriculture market. Grain elevators in coastal Texas have not been significantly damaged, but loading for export has halted as they are unable to receive supplies due to closure of flooded rail lines in the Houston area.

Cattle and cotton have also been affected, as Texas is the Number One producer of each.

Some 27 percent of the state’s 4.46 million-head beef cow herd resides in the disaster area and cotton crop losses are estimated around US$150 million, though the vast majority of cotton production takes place in the Panhandle, out of the storm’s path.

Harvey’s remnants are now moving into the US Delta states, where 20 percent of the nation’s cotton and 15 percent of soybeans are grown. Soybean harvest has just begun in the far south areas, but parts of the region could receive up to 8 inches (20 centimetres) over the next five days.

Active Season Predicted

The hurricane threat in the North Atlantic Basin is far from over, though. Back in May, forecasters at the National Hurricane Center gave the 2017 Atlantic hurricane season – which began on the 1^st June – a 45 percent chance of featuring above-normal activity. In its update on the 9^th August, NHC bumped these chances to 60 percent and noted “the possibility that the season could be extremely active.”

Forecasters point to a few primary reasons. One is that the large-scale climate indicator El Niño-Southern Oscillation – or ENSO – has much higher chances of sustaining neutral conditions through the end of the year rather than trend towards the warm phase El Niño as earlier forecasts suggested.

El Niño often suppresses tropical storm development in the North Atlantic since it features greater atmospheric stability and stronger winds that make it difficult for big, organised storms to form. ENSO’s cool phase, La Niña, usually promotes a favourable environment for tropical development in the Atlantic.

Additionally, sea surface temperatures in the key formation region of the ocean are warmer than models had previously predicted and the West African monsoon is stronger. Tropical cyclone formation in the North Atlantic often begins with an atmospheric wave off the African coast and most generally, warmer waters provide more fuel to the storm.

As of the 31^st August, there have been nine named storms in the North Atlantic Basin – above the long-term average of five for the date – so the season has been more active than normal so far, including a rare April-forming tropical storm.

NHC forecasters also mention that the enhanced early-season activity back in June and July in the tropical Atlantic usually suggests an above-average season ahead.

The climatological peak of the Atlantic hurricane season is the 10^th September and the season officially ends on the 30^th November. Activity can persist into December, but these storms usually never make it to hurricane status and have occurred only a handful of times in the last couple decades.

During August and September, all coastal areas along the Gulf of Mexico and Atlantic Ocean are historically susceptible to tropical cyclones which could make landfall. Into October and beyond, this threat tends to focus more on Florida and the Eastern Seaboard rather than the Gulf.

But to have another storm as severe as Harvey anytime soon may be unlikely, as Harvey was statistically rare. It was only the fifth hurricane in the last 50 years to make landfall in the United States with Category 4 strength or greater, with the last one being Charley in 2004.