31 August 2017

Two new tropical threats are taking shape in the Gulf of Mexico and Atlantic Ocean

The latest on Category 2 Hurricane Irma and the threat of development in the western Gulf of Mexico next week is available on the Capital Weather Gang blog:

Two new tropical threats are taking shape in the Gulf of Mexico and Atlantic Ocean


30 August 2017

After disastrous rain around Beaumont and Port Arthur, Harvey surges inland

I did not have a chance to write a full update on Harvey today, but it made another landfall in the early morning hours near Cameron, LA.  Extremely heavy rain sat over the Beaumont and Port Arthur (TX) area for hours, producing even worse flooding than what Houston experienced.

Radar and satellite images from the second landfall:
https://twitter.com/BMcNoldy/status/902828833690222593

Archived and ongoing long radar loops:
http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/

A more detailed update on Tropical Storm Harvey, written by Capital Weather Gang editor and colleague Jason Samenow is available at:

After disastrous rain around Beaumont and Port Arthur, Harvey surges inland



Tropical Storm Irma forms in Atlantic, and still watching Gulf of Mexico early next week

An update on newly formed Irma in the far eastern Atlantic and the potential for another storm early next week in the Gulf of Mexico is on the Capital Weather Gang blog:

Tropical Storm Irma forms in Atlantic, and still watching Gulf of Mexico early next week


29 August 2017

Forecasters warily watching the eastern Atlantic and Gulf of Mexico for new tropical storms

Aside from Harvey, there are other areas of the Atlantic basin that need to be watched closely... my second update today focuses on these two systems and is available on the Capital Weather Gang blog:

Forecasters warily watching the eastern Atlantic and Gulf of Mexico for new tropical storms


Maps of rainfall totals in Texas look like maps of snowfall totals after a Nor'easter

Rainfall totals from Friday morning through Tuesday morning. (SERCC)
As we enter Day 5 of heavy rain in Texas, the totals are staggering and still accumulating.  As of late Tuesday morning, several stations are referenced in a NWS list that are now at over three feet of rain:

MARYS CREEK AT WINDING ROAD      49.20
CEDAR BAYOU AT FM 1942           48.64
CLEAR CREEK AT I-45              47.20
DAYTON 0.2 E                     46.08
SANTA FE 0.7 S                   45.02
HORSEPEN CREEK AT BAY AREA BLVD  44.96
FRIENDSWOOD 2.5 NNE              42.76
PASADENA 4.4 WNW                 42.58
HOUSTON WEATHER FORECAST OFFICE  42.11
WEBSTER 0.4 NW                   41.77
LEAGUE CITY 2.7 NE               41.66
BAY AREA BLVD AT HORSEPEN CR     40.64
BERRY BAYOU AT NEVADA            40.32
BERRY B FOREST OAKS              40.28
VINCE BAYOU AT PASADENA          39.29
LITTLE VINCE BAYOU AT JACKSON    39.00
TURKEY CK AT FM 1959             37.96
MIDDLE BAYOU GENOA RED BLUFF     37.76
AMAND BAYOU AT NASA ROAD 1       37.68
JACINTO CITY                     37.60
LITTLE CEDAR BAYOU AT 8TH ST     37.32
TELEPSEN                         36.60
FIRST COLONY 4 WSW               36.34
BEAMER DITCH HUGHES RD           36.32
LA PORTE 1 N                     36.24
TAYLOR LAKE AT NASA ROAD 1       36.23

The report of 49.2" became the all-time record holder for highest rainfall amount associated with a landfalling tropical cyclone in the continental United States. The previous top three in the U.S. were...

Amelia 1978: 48.00" (Medina, TX)
Easy 1950: 45.20" (Yankeetown, FL)
Claudette 1979: 45.00" (Alvin, TX)

Storm-total rainfall maps for Amelia 1978, Easy 1950, and Claudette 1979. (David Roth, NOAA/WPC)
The accumulation map looks more like inches of snow after a strong Nor'easter, not inches of rain in a few days. A huge area is blanketed (or submerged in this case) by totals of 1 foot or greater.  Maxima are now over 4 FEET!!

The primary reason for these incredible amounts is that Harvey has barely moved.  The center is now just 150 miles from where it made landfall on Friday night.  It has also been a tropical storm or hurricane for 84 hours AFTER making landfall. If you add up all of the time it was a named storm prior to landfall (including the eastern Caribbean part) you get 90 hours.  Later today, it will have spent more time as a tropical storm or higher after landfall than it did prior to landfall.

Typically, storms make landfall and keep moving.  People have calculated bulk averages for "typical" rainfall amounts from landfalling storms.
 - In the late 1950s, R. H. Kraft introduced a rough guideline for maximum rainfall totals from a landfalling tropical cyclone: divide 100 by the forward speed of the storm in knots.  So for Harvey which was moving at 6 kts (7 mph) when it made landfall, you would get a maximum of 16.7 inches (if it kept moving at that speed).
 - David Roth (NOAA/WPC) created a chart using storms from 1991-2005 and found that the average landfalling storm produced 13.3 inches of rain.

(David Roth, NOAA/WPC)
But when a storm does not keep moving, these climatology-based estimates break down.  Or do they?  Using the Kraft rule, and Harvey's motion since landfall (150 miles in 84 hours = 1.6 kt), you would get a maximum of 64.4 inches.  We're still 14 inches shy of that extremely crude estimate, but it's also not over yet.
The forecast over the next 3 days still includes impressive totals over eastern Texas.


Today through Thursday, the flooding risk remains high in eastern Texas but also expands eastward to Louisiana, Mississippi, and Alabama.  Strong rainbands will affect these areas in the coming days as Harvey continues to tap into the endless moisture supply in the Gulf of Mexico.


With the center back over water now, it should draw in less dry air than it did on Monday, and a second landfall is forecast to occur on Wednesday afternoon near Lake Charles, LA. Tropical storm warnings and storm surge watches cover much of coastal eastern Texas and Louisiana.  The storm is expected to finally get kicked out of the area on Thursday then accelerate off to the northeast.




28 August 2017

Tropical storm warning for N.C. Outer Banks as Irma may soon form

The update on a disturbance off the northeast Florida coast is available on the Capital Weather Gang blog:

Tropical storm warning for N.C. Outer Banks as Irma may soon form


Tropical Storm Harvey moving back over water, new wave emerging from Africa

Since Sunday, Harvey has barely moved; in fact it has actually drifted back toward the south... back toward the warm Gulf water.  As of Monday morning, the center is indeed over water again... and Harvey has incredibly maintained tropical storm status continuously since making landfall on Friday night.



However, something that is sparing the hardest-hit areas for now is the storm's circulation is wrapping in drier air from the west which is greatly diminishing rainband development.



Models are in agreement that Harvey will re-intensify slightly over the Gulf of Mexico during the next couple of days before making another landfall on eastern Texas on Wednesday morning.  Given the current structure and dry air intrusion, it is very unlikely that Harvey will regain hurricane status... but the threat of heavy rain and additional flooding lingers.

The Houston area could receive at least another 20 inches of rain, on top of the 25-30 inches that has already fallen there. The flood risk will also migrate eastward into Louisiana this week. As the National Weather Service stated on Sunday morning, "This event is unprecedented and all impacts are unknown & beyond anything experienced."



The tropical disturbance I've been discussing for the past couple of weeks that approached south Florida last week is finally moving along, and may also finally become a named storm as it heads for the Carolinas.  My update on what may become Tropical Storm Irma will be on the Capital Weather Gang blog later today, and I'll have a separate post on that... stay tuned.

Much further east, a new healthy tropical wave has just exited the African coast — model guidance indicates that there is a good chance it will become the next named storm later this week (Irma if the Carolinas low doesn’t get it first, or Jose if it does).



Over the past 50 years, the average date for formation of the ninth named storm is September 30, and the tenth is October 14.  In terms of Accumulated Cyclone Energy, or ACE, the season is now at 97 percent of average for this date.



27 August 2017

Forecasts of Harvey's impact have been spot-on, which is really bad news for Texas

Since last Tuesday, the key message associated with Harvey was that historic rainfall and catastrophic flooding was expected over a large area in eastern Texas.  That message remained steady, even when Harvey was a tropical depression, and through its Category 4 hurricane landfall.  Unfortunately, now we are seeing the beginnings of that outlook come to fruition.

Overnight, the Houston area experienced unimaginably heavy rain, over 20 inches in some places in just a few hours.  The city is literally underwater today.  And there are days more of rain to come.  This is far from over.

Rainfall totals from Friday morning through Sunday morning.
Harvey is still forecast to remain stationary for the next few days... perhaps starting to drift northward on Wednesday.  The heavy rainfall we've been seeing is not going to end anytime soon.  The forecast for the next five days shows that areas around Houston could see an additional 1-2 feet of rain.


As of Sunday morning, Harvey is still a tropical storm with 45mph winds, and is centered about 65 miles east-southeast of San Antonio, 130 miles west-south of Houston, and 80 miles north of Corpus Christi.  But the specific storm center is not the concern, it's the sprawling rainbands that extend outward for hundreds of miles. Since the storm is still so close to water, the circulation is drawing in tropical moisture from the steamy Gulf of Mexico... an endless fuel source.


Aside from the torrential rain that rainbands produce, they are also well-known to produce tornadoes.  At least a dozen tornadoes have been reported in eastern Texas and western Louisiana since Saturday morning.

The latest forecast and warnings can be found on the National Hurricane Center website.  I have long regional radar loops available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/

There have been the usual "this came out of nowhere" and "we didn't think it would be this bad" statements from officials.  This is very unfortunate and irresponsible... this event was very well forecast and advertised for several days in advance.  Forecasts of widespread 15-20" totals with some areas seeing 40 inches or more will verify.

As someone who tries to get this information out, it's frustrating and infuriating when people who should know better claim they had no warning.  The general public seems to fear the category rating of a storm more than the rainfall forecast, yet rain is historically responsible for 3.3 times more fatalities than wind for hurricanes hitting the United States.  Storms like Harvey may help to make the public more aware that rain is a very big deal, even though it's not a part of the Saffir-Simpson category rating.

To give an idea of how consistent the messaging has been, here are some quotes from my posts since Friday the 18th (still lots of uncertainty on the 18th):

Aug 18: "Beyond the Yucatan peninsula encounter, things get hazy... but the possibility exists that it could become a hurricane in the Gulf of Mexico in about a week."

Aug 22: "Even if Harvey does not reach hurricane intensity, the rainfall associated with it is still expected to be a big problem. Over coming week, large areas from the Mexico border over to the north-central Gulf coast could see very substantial rainfall totals."

Aug 23: "By far, the hazard of greatest concern with this system is its rainfall. While the center of the storm is expected to reach the coast Friday afternoon, heavy rain is likely to begin in the morning. Because of weak atmospheric steering currents, computer models indicate Harvey will stall over the Texas-Louisiana area through most of the weekend, at least, dispensing potentially incredible amounts of rain. ... Some computer model forecasts suggest the storm could linger over Texas through early next week, producing astronomical rainfall amounts between 30 and 50 inches in areas."

Aug 24: "In addition to damaging winds, the National Hurricane Center said it expects “catastrophic and life-threatening” flash flooding along the middle and upper Texas coast. An incredible amount of rain, 15 to 30 inches with isolated amounts of up to 40 inches, is predicted because the storm is expected to stall and unload torrents for four to six straight days. In just a few days, the storm may dispense the amount of rain that normally falls over an entire year, shattering records."

Aug 25: "The impacts from this storm are anticipated to be almost unfathomable.  A storm of this intensity would be bad enough, but all guidance suggests that it will stall for several days right near the coast due to a lack of mid-level steering winds.  The rainfall forecasts are ominous, and if they come even close to verifying, this will be a storm for the history books. In this map below, which shows the cumulative rainfall forecast over the coming week, a large area is saturated at the >20 inches contour, but specific locations could see 3-4 FEET of rain.  Widespread and prolonged life-threatening flooding appears inevitable."

Aug 25: "Hurricane Harvey could be on par with 2005’s Hurricane Katrina in terms of economic impact. The Houston area and Corpus Christi are going to be a mess for a long time."

Aug 26: "A stationary tropical cyclone is a very bad thing... and widespread life-threatening flooding is anticipated over the coming days.  The latest 5-day rainfall forecast places over 20 inches of rain in the same areas that have been getting heavy rain since Friday morning. Locations within this area could see up to 40 inches.  Flooding might not be as dramatic as a hurricane making landfall, but it's more deadly."

The point of rehashing this is certainly not to say "I told you so", but rather to discredit the irresponsible and inaccurate messages coming out now that the event is actually happening.  This did not catch anyone offguard.  It could be the greatest flooding disaster in U.S. history.


26 August 2017

Harvey made landfall as Category 4 hurricane, but the disaster is far from over

At about 10pm local time on Friday, Harvey made landfall near Rockport, TX.  It rapidly intensified for two days leading up to landfall, and ended up crossing the coastline with 130 mph winds... a Category 4 hurricane.  It was the strongest hurricane hit the U.S. since Charley in 2004, and the strongest hurricane to hit Texas since Carla in 1961.

Infrared satellite image of Hurricane Harvey at the time of landfall.
Just two days prior to this, Harvey was a tropical depression with 35 mph winds.  Although it was forecast to become a hurricane by landfall, this extreme rate of intensification is unpredictable.  Hurricane watches were issued on Wednesday morning for the appropriate section of coastline... that is the maximum lead time used in tropical cyclone watches.
Hurricane watches were issued for Texas coast on Wednesday morning for a forecast landfall on Friday night.  Harvey was a tropical depression at this point.
As of early Saturday afternoon, Harvey is still a Category 1 hurricane and has already stalled over Texas.  It's extremely important that people in the area do not breathe a sigh of relief now that landfall is behind them.

Regional radar image from midday Saturday.
The big story has been and still is the rain.  This part of the event is just beginning to unfold.  The forecast still calls for Harvey to remain essentially stationary for at least the next five days.  From Friday morning through Saturday morning, rainfall totals are already impressive, especially in areas just north of Corpus Christi.  I have numerous long radar loops available at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/

Observed rainfall totals from midday Friday through midday Saturday.
A stationary tropical cyclone is a very bad thing... and widespread life-threatening flooding is anticipated over the coming days.  The latest 5-day rainfall forecast places over 20 inches of rain in the same areas that have been getting heavy rain since Friday morning. Locations within this area could see up to 40 inches.  Flooding might not be as dramatic as a hurricane making landfall, but it's more deadly.

Cumulative rainfall forecast over the coming five days.
Like most major hurricanes, Harvey originated from Africa.  The easterly wave that went on to become Harvey left the African coast on August 12 and was a trackable feature and/or tropical cyclone the entire time.  Storms like this do not come out of nowhere.


Harvey was also the first major hurricane to hit the United States since Wilma in 2005, so it ended the astounding record span of nearly 12 years between such landfalls.




25 August 2017

Harvey will probably make landfall as a ‘major’ hurricane. Here’s what that means.

You often hear the term "major hurricane", and may be confused that storms like Ike (2008) and Sandy (2012) were not major hurricanes at landfall.  A brief explanation is on the Capital Water Gang blog:

Harvey will probably make landfall as a ‘major’ hurricane. Here’s what that means.


Harvey nearly a major hurricane as it heads for Texas landfall tonight

At 8am EDT on Friday, the National Hurricane Center upgraded Hurricane Harvey to a Category 2 storm with peak winds of 110 mph. It is the third hurricane of the season and is extremely close to becoming the first major hurricane of the season (115mph+).  Landfall is forecast to be near Corpus Christi late Friday night into the early morning hours on Saturday.


Impacts on Texas have already begun and conditions will deteriorate throughout the day.  The central pressure as of 8am EDT is 950 mb and still falling - Harvey's dramatic intensification has not slowed down yet.  The eye is about 140 miles from Corpus Christi, but rainbands are already affecting the Texas coast, and tropical storm force winds will arrive by later in the morning.


The impacts from this storm are anticipated to be almost unfathomable.  A storm of this intensity would be bad enough, but all guidance suggests that it will stall for several days right near the coast due to a lack of mid-level steering winds.  The rainfall forecasts are ominous, and if they come even close to verifying, this will be a storm for the history books. In this map below, which shows the cumulative rainfall forecast over the coming week, a large area is saturated at the >20 inches contour, but specific locations could see 3-4 FEET of rain.  Widespread and prolonged life-threatening flooding appears inevitable.


In addition, the storm surge will be significant near the landfall location and for hundreds of miles to the right/east.  This impact will be exaggerated around the times of the normal astronomical high tides, but areas near the landfall point could see inundation levels of 6-12 feet.


As I said for an Associated Press interview yesterday, "Harvey combines the worst attributes of nasty recent Texas storms: The devastating storm surge of Category 2 Hurricane Ike in 2008; the winds of Category 4 Hurricane Bret in 1999 and days upon days of heavy rain of Tropical Storm Allison in 2001."

I have a series of long, updating radar loops to cover Harvey at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/radar/, and as of this writing (8am EDT), this is the view from the Corpus Christi radar:


For the latest information and updates on storm intensity, watches, warnings, forecasts, etc, consult the National Hurricane Center.  You can also follow frequent updates on the Capital Weather Gang blog.

The last hurricane to make landfall on Texas was Ike in 2008 (9 years ago), and the last major hurricane to make landfall on Texas was Bret in 1999 (18 years ago).

If Harvey strengthens just slightly by landfall, it will be the first major hurricane to make landfall on the United States since Wilma in 2005, a record-smashing 4323 days ago.  A major hurricane is defined to be one that is a Category 3 or higher on the Saffir-Simpson scale (115mph+ sustained winds). This "major hurricane drought" has largely been due to pure luck.  Other countries have been hit by major hurricanes since then, and the U.S. has had some close calls.


Since Wilma, the U.S. has been hit by ten hurricanes, all Category 1 and 2 storms... though some were certainly still significant and destructive.  The list includes:
Humberto 2007
Dolly 2008
Gustav 2008
Ike 2008
Irene 2011
Isaac 2012
Sandy 2012 (not technically a hurricane at landfall)
Arthur 2014
Hermine 2016
Matthew 2016

A key message here is that it does not take a major hurricane to cause a tremendous amount of damage.  Storm surge and rainfall are big players even in weaker storms, but major hurricanes add extremely strong winds to the mix. "There's more to the story than the category".


24 August 2017

Rapidly strengthening Harvey forecast to slam east Texas as major hurricane and stall

All eyes are on Harvey, which is poised to become the season's third hurricane today, as it heads for landfall in Texas on Friday, and could still be over Texas on Tuesday.  Update on the Capital Weather Gang blog:

Rapidly strengthening Harvey forecast to slam east Texas as major hurricane and stall


23 August 2017

Hurricane watch issued for Texas as Harvey reforms, tremendous rainfall possible

Harvey, which exited the African coast as an easterly wave back on August 12th, became the season's 8th named storm on the 17th, then dissipated to an open wave on the 20th, has just been re-upgraded to a tropical depression on the 23rd.  My update on the storm and the very dangerous situation that is expected to develop in Texas and Louisiana is on the Capital Weather Gang blog:

Hurricane watch issued for Texas as Harvey reforms, tremendous rainfall possible


22 August 2017

18 August 2017

Tropical Storm Harvey forms and enters the Caribbean, closing watching the disturbance behind it

Tropical Storm Harvey and Invest 92L on Friday morning. (CIRA/RAMMB)
A tropical wave east of the Lesser Antilles was upgraded to Tropical Storm Harvey on Thursday afternoon... the eighth named storm of the season.  It is now crossing into the Caribbean Sea and is expected to intensify as it heads west.  There are tropical storm warnings for the Windward Islands, which should be allowed to expire later today as it moves away.  The primary threat is heavy rain causing mudslides and/or flooding.


Model agreement is very tight on the forecast track: it will reach Belize and the Yucatan peninsula on Tuesday-Wednesday and very likely as a strong tropical storm or Category 1 hurricane.  It will affect the same areas that Franklin did two weeks prior.  Beyond the Yucatan peninsula encounter, things get hazy... but the possibility exists that it could become a hurricane in the Gulf of Mexico in about a week.  At this point, it's just something to be aware of, not concerned about.

Elsewhere, the tropical wave right behind (east) of Harvey is also a feature of interest.  Currently termed Invest 92L, it would become Tropical Depression Ten or Tropical Storm Irma if/when it develops into a tropical cyclone -- maybe today?


Since it is centered a few hundred miles further north than Harvey, the steering currents are also different -- and rather than cruising westward through the Caribbean, it is forecast to track toward the west-northwest through the next five days.  That trajectory brings it near south Florida late Tuesday into Wednesday.


However, as of now, none of the reliable global or regional models do much of anything with it in terms of intensity.  When it arrives in the vicinity of south Florida on Tuesday into Wednesday, it is an open wave in model-land, having been weakened by mid-level dry air and moderate shear.  Those days could still be breezy and stormy, but given the current guidance, it is not expected to be anything too noteworthy.

But it's important to point out that there is some risk associated with placing so much confidence in models.  We are looking at a tropical disturbance, maybe even a tropical cyclone, tracking over the Bahamas and toward south Florida in the 4th week of August... climatology would not suggest completely dismissing the threat which would be just four days away from now.  South Floridians should be watching this one closely.

Also, since my last update on Monday, Gert did indeed reach hurricane intensity, and was actually a Category 2 hurricane for 18 hours as it recurved into the north central Atlantic.  It has been absorbed into an  extratropical cyclone, but was the season's second hurricane and the strongest storm of the season so far.

In terms of seasonal metrics, we are at eight named storms, two hurricanes, and no major hurricanes, with an Accumulated Cyclone Energy (ACE) of 16.2.  Using the past fifty years as climatology, the average for this date is three named storms, one hurricane, no major hurricanes, and an ACE of 14.9.  The last time there were this many named storms at this point in the season was 2012, and before that: 2005.  Both were extremely active seasons.




14 August 2017

Gert may become season's second hurricane... watching deep tropics for possible Harvey

An African wave that I first mentioned on August 4th was upgraded to Tropical Depression 8 and then to Tropical Storm Gert over the weekend (it exited Africa on the 3rd).
Elsewhere, eyes are on a new wave that just exited the African coast on Saturday.  This is nothing to be concerned about now, just something to keep an eye on.  The next name on the list is Harvey.

An update on these two systems can be found on the Capital Weather Gang blog:

Tropical Storm Gert may become this season’s second Atlantic hurricane