Raleigh News & Observer Logo

Tropical, subtropical, non-tropical... what's the difference? | Raleigh News & Observer

×
  • E-edition
    • Customer Service
    • Support
    • Contact Us
    • About Us
    • FAQ
    • Sponsorships
    • Stay connected
    • Mobile & Apps
    • Facebook
    • Google+
    • Instagram
    • Twitter
    • Social Media Directory
    • N&O Store
    • Buy Photos
    • Databases
    • Archives
    • Newsletters

    • Blogs
    • Columnists
    • Crime
    • Education
    • Health
    • Local
    • North Carolina
    • Nation/World
    • Science
    • Thumbs Up
    • Traffic
    • Weather
    • Weird News
    • All News
    • Counties
    • Durham County
    • Johnston County
    • Orange County
    • Wake County
    • All Sports
    • Baseball
    • Canes
    • College
    • Columns & Blogs
    • High Schools
    • NASCAR & Auto Racing
    • NBA
    • NFL
    • NHL
    • Olympics
    • Outdoors
    • Panthers
    • Soccer
    • Schools
    • Duke
    • East Carolina
    • NC State
    • North Carolina
    • All Politics
    • The North Carolina Influencer Series
    • State Politics
    • Blogs
    • Columnists
    • PolitiFact
    • PolitiFact NC
    • Rob Christensen
    • Under the Dome
    • All Business
    • Blogs
    • Columnists
    • Health Care
    • Personal Finance
    • Real Estate
    • Shop Talk
    • Stocks Center
    • Technology
    • All Living
    • Video Now
    • Best-Kept Secrets
    • Blogs
    • Celebrations
    • Comics
    • Family
    • Fashion
    • Fitness
    • Food
    • Games and Puzzles
    • Home and Garden
    • Horoscopes
    • Mouthful
    • Past Times
    • Pets
    • Religion
    • Travel
    • Video Now
    • Arts News
    • ArtsNow
    • Books
    • Contests
    • Dining
    • Entertainment
    • Games
    • Movies
    • Music
    • Nightlife
    • Television
    • On the Beat
    • Happiness is a Warm TV
    • All Opinion
    • Columnists
    • Dwane Powell
    • Editorials
    • Influencers Opinion
    • Letters
    • Opinion Shop Blog
    • Other Views
    • Submit a Letter
  • Obituaries

    • Advertise with us
    • Place Ad
    • Apartments
    • Cars
    • Homes
    • Jobs
    • Legals
    • Obits/In Memoriams
    • Weddings
    • Today's Daily Deal
    • Special Sections
    • Today's Circulars
    • Rewards
    • Photo Store
  • Classifieds
  • Jobs
  • Moonlighting
  • Cars
  • Homes
  • Legals

Clear Weather

Tropical, subtropical, non-tropical... what's the difference?

By Niki Morock

nmorock@newsobserver.com

    ORDER REPRINT →

May 08, 2015 02:15 PM

If you've been paying attention to the ever-changing weather reports for the past few days, you've probably noticed meteorologists and reporters saying "tropical low," "non-tropical low," and "subtropical low" or "cyclone" or any variation in trying to describe the storm now known as Ana. For the casual observer, it may seem like we don't know what to call this storm brewing off our coast. The truth is that for a while there, we didn't.

Forecasting for low pressure systems that develop off the southeastern coast in the Atlantic this time of year can be tricky. A truly tropical storm needs ocean temperatures near 80º or warmer, which usually don't occur until the summer months. This is the reason hurricane season starts in June.

When forecasters first noticed the computer models showing a coastal low pressure system developing this week, it would have been easy to assume that in early May with the sea surface temperatures mostly in the 70s, the storm would struggle to become tropical in nature. Even the warmer waters of the Gulf Stream current are just barely near that threshold. So, initially meteorologists were saying that a coastal low or non-tropical cyclone or, at best, a subtropical storm would develop near Florida in the Atlantic. The path of the storm was also in question since it hadn't developed yet. Farther out to sea and away from the Gulf Stream, it would not have much of an effect on land, but closer to the coastline, it could have a major effect.

A subtropical storm could be thought of as a hybrid of a plain Jane storm that develops over cooler waters that would likely never become a hurricane and a tropical storm. Subtropical storms can begin anywhere between the equator and 50º latitude, and they require enough warm water to create convection (thunderstorms). Remember that with thunderstorms, heat is the source of their power. Subtropical storms tend to produce a little wind and a decent amount of rain.

Sign Up and Save

Get six months of free digital access to The News & Observer

SUBSCRIBE WITH GOOGLE

#ReadLocal

Tropical storms can strengthen to become hurricanes, and require the above mentioned warm ocean temperatures, an initial disturbance, and time to get organized. Tropical storms need to keep moving in order to gain strength. If they stay in the same place, they begin to bring colder water up from the depths of the ocean to replace the warmer water at the surface that they use to fuel themselves. In essence, they commit suicide by standing still.

Storms with tropical characteristics can be named. When the forecasters at the National Hurricane Center saw that Ana's path would take her over the Gulf Stream long enough to develop thunderstorms and a closed circulation, they named her. Even though it is early May, we have our first named storm of the season. The expectation is for Ana to become a tropical storm with wind speeds near 40 mph and very little strengthening beyond that before making landfall.

Sustained winds of 40 mph could blow yard debris around and cause some issues with high profile vehicles among other things. The major concerns with Ana are the storm surge caused by the wind, rainfall of 2-6 inches, and dangerous surf conditions. The storm surge will combine with high tide and should cause some flooding near the coast with water rising 1-2 feet above where it normally would.

Here in the Triangle, expect a showery Mother's Day weekend as Ana invites herself to the celebration. Make sure to have a backup venue to any outdoor plans you've made, especially on Sunday when the greatest chance for rain arrives. Saturday may not be a total wash-out. In fact, we could see some sun in the early afternoon, but the chance for storms increases as the day goes on. Even with the increased rain probabilites this weekend, we may only see 1/10 to 1/2 inch of rain with a bit more embedded in thunderstorms. The worst of the rain will be restricted to the coast.

Related stories from Raleigh News & Observer

weather

Subtropical Storm Ana moving towards the NC coast

May 08, 2015 01:27 PM

  Comments  

Videos

Tropical depression expected to become Tropical Storm Nate

NC State’s Wyatt Walker talks about his ‘havoc’ hair

View More Video

Trending Stories

John Harris warned his father about legal red flags involving Bladen operative

February 20, 2019 02:13 PM

Zion Williamson injured during Duke-UNC game after foot blows through shoe

February 20, 2019 09:53 PM

Zion Williamson injured as No. 1 Duke falls to No. 8 UNC

February 20, 2019 11:11 PM

Transgender woman has asked to be moved from a men’s prison. So far, NC has said no.

February 20, 2019 01:42 PM

Three observations from No. 8 North Carolina’s 88-72 road win over No. 1 Duke

February 21, 2019 02:18 AM

Read Next

Why meteorologists look at ALL of the models

Clear Weather

Why meteorologists look at ALL of the models

By Niki Morock

nmorock@newsobserver.com

    ORDER REPRINT →

October 05, 2016 03:04 PM

While some weather forecast models are better than others, I want folks to really understand that all have their strong points and shortcomings.

KEEP READING

Sign Up and Save

#ReadLocal

Get six months of free digital access to The News & Observer

SUBSCRIBE WITH GOOGLE

MORE CLEAR WEATHER

Clear Weather

Did we learn anything from Katrina?

August 25, 2015 04:42 PM

Clear Weather

Hello, Tropical Depression Four!

August 18, 2015 01:56 PM

Clear Weather

Nature doesn't need photo editing

August 12, 2015 12:14 PM

Clear Weather

Airlines help improve weather forecasts

August 05, 2015 03:47 PM

Clear Weather

Recognizing a rip current can save your life

July 31, 2015 04:38 PM

Clear Weather

Why isn't the Southeast warming as fast as the rest of the Earth?

July 22, 2015 02:51 PM
Take Us With You

Real-time updates and all local stories you want right in the palm of your hand.

Icon for mobile apps

Raleigh News & Observer App

View Newsletters

Subscriptions
  • Start a Subscription
  • Customer Service
  • eEdition
  • Vacation Hold
  • Pay Your Bill
  • Rewards
Learn More
  • About Us
  • Contact Us
  • Newsletters
  • News in Education
  • Triangletoday.com
  • Legal Notices
Advertising
  • Advertise With Us
  • About Our Ads
  • Place a Classified
  • Local Deals
  • N&O Store
  • N&O Photos
Copyright
Commenting Policy
Report News
Privacy Policy
Terms of Use


Back to Story