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From Maryland to the Caribbean to Asia, Record-Hot Ocean Waters Give Extreme Weather Potentials a Big Boost

The forecasts began coming in this morning: Heavy rainfall expected over the next two days. Possible flash flooding. Turn around, don’t drown.

These advisories buzzed up from local news media for the DC, Maryland, and Northern Virginia metro areas as a crazy, wavy Jet Stream spawned an upper-level low that’s predicted to gorge on an insane amount of moisture spewing up off the record-hot Atlantic Ocean.

Forecast GFS model guidance shows an upper-level low-pressure system situated over the Great Lakes region in association with a big trough dipping down from the Arctic. Over the next 24 to 48 hours, the low is expected to shift south and east. Becoming cut off from the upper-level flow, the low is then predicted to set up a persistent rainfall pattern over DC, Maryland and Northern Virginia.

noaa-extreme-rainfall-dc-metro-area

(NOAA’s precipitation forecast model shows extreme rainfall predicted for the DC area over the next seven days. Note that record global heat and, in particular, excessively hot sea-surface temperature anomalies off the U.S. east coast are providing an unprecedented amount of fuel for storms. Should such storms fire off, they could produce rainfall totals in excess of those currently predicted. Image source: NOAA.)

Easterly winds are expected to be drawn into the low from a record-hot Atlantic Ocean. These winds will bear upon them an extraordinary burden of atmospheric moisture which has been continuously evaporating up from a very warm Gulf Stream. Such moisture is fuel for powerful rainstorms. Given the destabilizing kick provided by the upper-level low, it is expected to deliver some pretty intense downpours on Wednesday, Thursday and Friday.

NOAA model guidance shows rainfall amounts of 3 to 6 inches over the area for the next five days. However, given the high atmospheric moisture content and the record atmospheric and ocean heat that’s spiking storm energy potentials, there is a possibility for locally higher amounts.

Extreme Ocean Heat Contributes to Severe Weather

As the DC area prepares for what could be another record or near-record rainfall event, various other regions over the Atlantic and on the other side of the world are also facing the possibility of intense weather. Very warm sea-surface temperatures are the common thread that links all these events.

atlantic-ocean-heat

(Hot sea surfaces are loading up the atmosphere with moisture and helping to produce convective updrafts that heighten storm tops. Such are the results of climate change, which has now dumped an extraordinary amount of heat energy into the Earth’s ocean and atmosphere — energy that now provides fuel for both extreme rainfall events and more-intense hurricanes. Image source: Earth Nullschool.)

In the Atlantic Ocean, just off Maryland and DC, sea-surface temperatures running at an amazing 5.7 degrees Celsius above average are helping fuel this week’s possible extreme rainfall event. For reference, ocean temperatures over the course of the 20th century tended to range between 2 C above average to 2 C below average. Any deviation beyond a 2 C departure for any significant length of time was considered pretty out of the ordinary. But off the U.S. east coast over the past couple of years and concurrent with record-hot global temperatures, sea surfaces have regularly hit such high ranges. The heat bleeding off those waters has contributed to a growing number of intense precipitation events.

Possible Strong Cyclone to Form in Caribbean, Track Toward U.S. Coast

Farther south, the Caribbean is also quite hot. Ranging from 1-2 C above average, this region of warmer-than-normal ocean water is about to receive a strong tropical wave running in from the east. Over the next week, this wave is expected to gorge on these hot waters, firing off intense thunderstorms with rising tops around a tightening center of circulation, and developing into a tropical cyclone that could reach hurricane strength by late this week or early next week. Long-range model runs predict all kinds of possible rough weather related to this potential storm for the U.S. east or Gulf coasts or even for the Canadian Maritimes.

florida-hurricane-october-7-ecmwf

(Most recent ECMWF model run shows an extremely powerful 938-millibar hurricane threatening southeast Florida on October 7. If such a storm does form, it will be fueled by hotter-than-normal ocean conditions brought about by human-caused climate change. Image source: Tropical Tidbits.)

One of the most accurate forecast models, the European Centre for Medium-range Weather Forecasting (ECMWF), is pointing toward the possibility of a major hurricane of 938-mb intensity threatening the southeast coast of Florida by October 7. Though such long-range forecasts are highly uncertain so far out, the underlying models are obviously picking up on the potential energy provided by all that ocean heat. The result is a kind of climate roulette — with a few extra bullets in the chambers. In other words, with all that ocean heat laying around, the potential for a big storm is just sitting there, waiting for something big to come along and suck it up. This ongoing, worsening situation could result in some serious added weather consequences over the next ten days or so.

Megi is Third Tropical Cyclone to Impact Taiwan

All across the world this year, big rainfall and related storm events have been popping up. Louisiana alone saw two 30-inch plus rainfall events while nearby Texas got hit again and again and again. This week, major floods in Iowa spurred officials to urge thousands to evacuate. Meanwhile, the recent Ellicott City, Maryland flood has people in the DC area on edge over this week’s potential for very heavy rainfall.

Half a world away today, Typhoon Megi roared ashore in Taiwan as a Category 4 tropical cyclone with top sustained winds of 132 miles per hour. Knocking out power for 3 million people across the island, the storm is now reported to have resulted in 250 injuries and the loss of 4 lives. Meanwhile, as much as 36 inches of rain has fallen over parts of the island.

It’s worth noting that rainfall hasn’t stopped over Taiwan yet, even as the massive circulation of Megi plows toward China — which is likely to receive heavy rainfall from the storm as well.

Like the possible extreme weather events related to very-hot surface waters in the North Atlantic and Caribbean, Megi formed over waters that are 1-3 C hotter than normal. But what’s a bit odd about Megi is that she followed almost in the exact tracks of two other cyclones — one which brushed by just to the north of Taiwan, and another which skirted the island’s south side. Typically, upwelling of cooler waters caused by hurricanes and tropical storms is enough to prevent an immediate follow-on by powerful systems, due to the fact that surface waters tend to be warmer than waters below the surface. But Megi followed these two systems and was able to tap enough ocean heat to reach Category 4 intensity even as it supported a massive outflow.

typhoon-megi-crosses-taiwan

(Typhoon Megi dwarfs Taiwan. Image source: Earth Observatory.)

How did this happen? Well, considering the fact that ocean surfaces in Megi’s path are still 1-2 C hotter than normal, it’s likely that the waters at depth were also much warmer than usual, meaning storm-related upwelling wasn’t able to limit the strength of follow-on storms. This possible new feature of the Western Pacific raises the strange potential for regions to be hit by a train of tropical storms and cyclones, as happened with Taiwan over the past couple of weeks.

Conditions in Context — Record-Hot Ocean, Atmosphere Fuels More Severe Storms

The common link between the forthcoming potential severe weather along the U.S. east coast and the intensity of Typhoon Megi upon following behind two other storms is increased ocean heat. Such heat acts as a kind of energy and moisture engine for more, and more powerful, storms, such as the aforementioned extreme rainfall events and powerful, peak-intensity cyclones. In short, these are aspects of a world undergoing fundamental climate shifts — shifts that continue to ramp up due to the great and ongoing emission of greenhouse gasses into the Earth’s atmosphere.

Links:

Heavy Rain, Flood Threat

GFS Model Guidance by Earth Nullschool

NOAA

Tropical Tidbits

Typhoon Megi Smashes into Taiwan on Path to China

Typhoon Megi Passes Taiwan

Thousands Urged to Evacuate Iowa Floods, Megi’s Threat to Taiwan Escalates

Scientific Hat tip to Dr. Jeff Masters

Hat tip to DT Lange

Hat tip to Colorado Bob

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For Louisiana, the Rains of Climate Change Fall Hard — More Heavy Storms Expected to Hit Central U.S.

Imagine, for a moment, that the Earth’s atmosphere is simply a big storm-generating engine. Imagine that the ignition trigger for this engine comes in the form of heat rising off the land and ocean surface. And imagine that the engine’s fuel is water vapor evaporated by that heat.

Keep the level of heat and water vapor constant, and you’ll get a continuous, steady stream of storms firing off. But increase the heat and water vapor content, as we have over the past 137 or so years, and the storms that engine produces become a whole hell of a lot more powerful.

In this context, in the last few days record atmospheric and ocean-surface heat helped to produce some of the highest water vapor levels ever recorded over Louisiana. This extreme moisture content, in turn, sparked some of the worst flooding ever seen for the state. From the Pacific Standard:

As the atmosphere warms thanks to greenhouse gas emissions, it can hold more water vapor — and this effect makes it exponentially more likely that extreme rainfall events will occur. The weather balloon released on Friday morning from the New Orleans office of the NWS measured near all-time record levels of atmospheric moisture, higher than some measurements taken during past hurricanes. The NWS meteorologist who reported this morning’s reading remarked simply, “obviously we are in record territory.”

By burning fossil fuels in such high volumes for so long, that’s what we’ve done. We’ve added heat and moisture fuel to the atmospheric engine such that historic, unprecedented rain events now seem to be a weekly occurrence. And the strength of storms hasn’t increased by only a bit: the strongest storms are now exceptionally more powerful than they were back before so much CO2 and other greenhouse gasses turned the Earth’s atmosphere into something the structures of human civilization aren’t really engineered to handle.

Amite River

(The Amite River hits highest crest ever recorded as sections of Louisiana see 20-30 inches of rain. Image source: NOAA.)

Today, the Earth’s atmosphere also has a bit more kick due to another contributing factor: The Earth is now cooling down from a strong El Nino that helped push the world to record-hot temperatures in 2015 and 2016. To be clear, this El Nino is not the cause of the record-hot global temperatures (nor of all the added extreme rainfall potential) — it’s the warm side of the natural variability cycle. However, when you add in human greenhouse gasses, each El Nino brings with it the risk of hitting new hottest temperatures ever. As those new hot temperatures are reached, the atmosphere gets another kick into a higher, more damaging storm-firing gear.

As El Nino cools toward La Nina, that heavy volume of extra moisture loses a bit of its atmospheric support. Imagine tons and tons of moisture held up only by the heat rising from below. Take some of that heat away, and a big portion of that huge volume of moisture is going to fall out somewhere as a big rain bomb. Over the past few days, these huge dumps of rain set their sights on Louisiana.

Louisiana Floods Worst Ever Recorded

About a week ago, a powerful flood of atmospheric moisture emerged from the record-hot surface waters of the Gulf of Mexico. Almost immediately, extremely strong storms bloomed, producing very heavy rainfall totals in the range of one foot or more along sections of coastal Florida and just offshore.

Over the course of the next few days, this big swirl of moisture, which in many ways resembled a tropical cyclone without the strong center of circulation, drifted west. By late Thursday, it began to move inland over sections of coastal Louisiana. It was then that the real inundation started. By Friday, reports were coming in that one foot of rain had already fallen in southeastern portions of the state. Throughout Saturday and Sunday, the rains just kept coming.

Historic Rainfall Louisiana

(Areas in blue on the precipitation map show regions that have received greater than one foot of rainfall over the past 72 hours. Note the huge swath in central southern Louisiana. Heavy storms have also hammered the central Mississippi River states and southeastern Texas. Image source: iWeatherNet.com.)

By early Monday, 72-hour rainfall totals showed that fully one-third of Louisiana had received more than one foot of rainfall (see map above). Local spikes within this huge swath have now exceeded two feet with total amounts as high as 30 inches reported.

As the heavy rains fell like never before, they pushed a historic flood of water down local rivers, many of which hit their highest levels ever recorded at various locations Sunday and Monday. As of Monday morning, the Amite River had crested six feet above the previous record high level at Magnolia and more than four feet above the all-time high at Denham Springs.

Currently, most of the eastern half of Baton Rouge and numerous adjacent communities are experiencing very severe flooding. There, 125 vehicles are reported stranded on Interstate 7 even as more than 1,000 homes have flooded. In Livingston, St. Helena Parish, and Tangipahoa Parish another 1,700 homes are reported to have flooded. With floods affecting operations, hospitals such as Ochsner Medical Center in Baton Rouge are being forced to transfer patients. Rail lines have been flooded out, telephone service cut off, and seven people are reported to have lost their lives with more missing.

Louisiana Homes Flooded

(Residents must use motor boats to access homes in southeastern Louisiana as around 20,000 residents have been forced to evacuate. Image source: KVEW.)

Throughout the region, more than 3,500 emergency personnel have been helping to evacuate those in the flood zone and hundreds have been plucked from the rising waters including a well-known college sports commentator and his wife. In total, more than 20,000 people and thousands of companion animals have now been rescued. Louisiana governor John Bel Edwards, who declared a state of emergency on Friday, watched aghast as his mansion’s basement flooded this morning, forcing him to join the displaced.

Unfortunately, storms continue to rumble over Louisiana, with one of these tossing out a lightning bolt that sparked a fire at a local oil refinery this morning (which was subsequently extinguished).

More Big Storms Predicted from Texas to the Great Lakes

Much of the moisture from the system that generated unprecedented flooding in Louisiana has since been pulled into a big trough stretching from Texas diagonally across the Mississippi into northeastern Ohio. Big storms are predicted to erupt along this frontal boundary today and tomorrow, with significant heavy rainfall expected.

Precipitation Map

(NOAA’s seven-day forecast shows very heavy storms from Texas to the Great Lakes. Image source: NOAA QPC.)

This precipitation pattern is predicted to remain mostly in place over the coming week as the frontal boundary stalls and then sags toward Tennessee. Areas expected to see heaviest precipitation totals range from Texas through northern Louisiana and into the Great Lakes region.

It’s worth noting that there’s still a huge amount of moisture in this system. So far, NOAA-predicted precipitation amounts have come up short of the heaviest amounts hitting local regions by as much as 50 percent or more, so unfortunately we’re likely to see more flash-flooding events over a broad area as the week progresses. With so much heavy precipitation falling along the Mississippi, it’s likely that a number of significant flood pulses will be headed toward portions of that large waterway.

Links:

Death Toll Rises in Historic Louisiana Floods — 20,000 Rescued

Historic Flood Event in Louisiana From 20-30 Inches of Rain

America’s Latest 500-Year Rainstorm

Total Rainfall Over Past 3 Days

Rain Bombs Set Sights on U.S. Gulf Coast

KVEW

NOAA QPC

NOAA Doppler Radar

iWeatherNet Weather Map

NOAA River Gauges

Hat tip to Bill McKibben

Hat tip to DT Lange

Hat tip to Colorado Bob

Hat tip to Jay M

Hat tip to Cate

Hat tip to Darvince

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