31 May 2018

As hurricane season begins, Colorado State lowers its prediction for the year

Today's post highlights the updated seasonal hurricane forecast from the pioneers of the science, Colorado State University... and formally introduces the names and products of the 2018 season (Alberto was a sneak peak!).

As hurricane season begins, Colorado State lowers its prediction for the year

30 May 2018

27 May 2018

Severe impacts from Subtropical Storm Alberto beginning in Florida and parts of the Southeast

Subtropical Storm Alberto is strengthening, and impacts are spreading to more areas.  Landfall is still expected on Monday morning. My Sunday morning update is available on the Capital Weather Gang blog:

Severe impacts from Subtropical Storm Alberto beginning in Florida and parts of the Southeast

25 May 2018

Subtropical Storm Alberto forms, kicking off hurricane season 1 week early

On Friday morning, the tropical disturbance we have been watching for what seems like forever was upgraded to Subtropical Storm Alberto, the first named storm of the 2018 Atlantic hurricane season.  It also makes 2018 the 4th consecutive year with a pre-season named storm, an unprecedented string.

Alberto is expected to transition to a fully tropical storm later, but as of now it does meet the criteria.  The difference between the two is really just academic, as it pertains to the structure of the system... not the impacts. If and when it becomes Tropical Storm Alberto, nothing will be magically different about it, other than the distribution of the wind field and perhaps the symmetry of the thunderstorms around it.  Cyclones come in many shapes and sizes across a spectrum!

Just as before it was named, the biggest impact will be extremely heavy rain over a large region.  The forecast 5-day rainfall totals are shown below:

Secondly, storm surge flooding will become a concern along Florida's west coast and along the northern-to-northeastern Gulf coast.

Models remain in pretty good agreement on the track and timing, but with any tropical cyclone, it's big, so impacts will extend far beyond the center line.  A series of 3-day track forecasts from dynamical models is shown below.  Wind shear should keep the system lopsided, so the messier, rainier side will be to the east of center, including the Florida peninsula.

Stay tuned to the National Hurricane Center website for the latest forecasts, watches, and warnings.

It is interesting to note that since 1851, only 3 other tropical cyclones formed within 200 miles of where Alberto is now during May (plus one in February 1952). All three May ones formed on May 31st!

24 May 2018

2018 likely to be 4th consecutive year with pre-season named storm: Alberto

The tropical system I mentioned in last Friday's update is indeed getting better organized in the western Caribbean.  Many models have been showing this for at least the past 10 days, so it comes as no surprise. As of Thursday afternoon, the system is centered inland over the eastern Yucatan peninsula and is tracking toward the north.

If this earns a name this weekend, which seems likely, it will be the unprecedented *4th* consecutive year with a pre-season named storm!  The first name on this year's list is Alberto.  (and coincidentally, the last time Alberto appeared in 2012 it was also a pre-season storm!)

Models have come into rough agreement on the track and timing of this potential tropical cyclone, but they still have differing opinions on the intensification.  Invest 90L, or "pre-Alberto", will head north through the central-to-eastern Gulf of Mexico this weekend. Water temperatures ahead of it are in the 27-28°C ballpark (80.5-82.5°F), which is plenty warm to fuel a tropical storm or a hurricane.

The system is embedded in a very moist envelope, so dry air wrapping into to the circulation shouldn't be an inhibitor. The biggest obstacle facing this nascent cyclone is vertical wind shear.  But even that may not be enough to stop it from intensifying by Saturday.  As of now, models agree on a Monday morning landfall as a strong tropical storm or possibly even a hurricane... somewhere between eastern Louisiana and the eastern Florida panhandle. The exact location doesn't matter though, as impacts extend far from the center.

Unfortunately, it's hard to trust the intensity details too much yet since it's currently not even a Depression. But as time goes on (and it escapes the influence of land), confidence in the model guidance will increase.

By far, the biggest concern associated with this is flooding caused by heavy rainfall.  Not only is very heavy rain expected in the northern Gulf coast region near the landfall location, but also over south Florida and up into Georgia and South Carolina in the coming week.

Depending on just how much this strengthens, the second-order concern will be storm surge along the west Florida coast and northeastern Gulf coast, so stay tuned!

On the topic of another pre-season named storm, I plotted up the formation date of the first named storm from the past 40 years.  A very obvious trend appears!  There may be a few reasons for this, but it's certainly interesting.

18 May 2018

Can't wait for hurricane season to start? You may not have to.

I have a brief update on a potential development in the western Caribbean Sea which could affect Florida next Friday-Saturday... it is available on the Washington Post's Capital Weather Gang blog:

Hurricane season technically starts June 1, but it could fire up early

12 April 2018

Four names retired from 2017 hurricane season, the most since 2005

In a recent meeting of the World Meteorological Organization (the agency that decides on tropical cyclone names), four names were retired from the 2017 list: Harvey, Irma, Maria, and Nate.  There is a series of six name lists that rotate every six years, so the same list we had in 2017 was also in place for 2011, 2005, 1999, etc, and will be used again 2023.

However, names can be permanently retired from use and replaced with different ones if the storm associated with that name was "so deadly or costly that the future use of its name on a different storm would be inappropriate for obvious reasons of sensitivity" (NHC). The new names in the 2023 list will be Harold, Idalia, Margot, and Nigel.

2017 was impressive in that more than three names were retired from a single season... the other such seasons were 2005 (5), 2004 (4), 1995 (4), and 1955 (4).

Irma was retired on its first time on a list (it replaced Irene from 2011).  The other names that were retired on their list debut were Igor (2010), Ike (2008), and Michelle (2008).  [Note that Joaquin first appeared on a list in 2009, but did not get used... it was retired after its first use in 2015.]

Having yet another retired "I" name amplifies that letter as the most commonly-retired (11 times)... "C" is in second place at 9 times.

And, not surprisingly, the most frequent month for a retired storm name to have occurred in is September.

Finally, although Category 5 storms are the strongest, they are rare... so the majority of names that get retired are from storms that peaked at Category 4 intensity.  But, notice that "major hurricanes" (Category 3 or higher) account for 84% of all retired names.

05 April 2018

April outlook for 2018 Atlantic hurricane season activity

As they have done every year since 1984, Colorado State University (CSU) has released their initial predictions for the upcoming Atlantic hurricane season. Phil Klotzbach and I take a look at the numbers in this post on the Washington Post's Capital Weather Gang blog: