Some Homegrown Tropical Problems?
All the focus recently has been on Hurricane, now Tropical Storm Bertha over the central Atlantic. It’s time to take a closer look at what has popped up not far off our coast this morning. A fairly well developed area of low pressure has spun up on the end of an old frontal boundary that has pushed offshore back at the end of the week. The low is clearly visible on satellite and QUIKSCAT images below. The QUIKSCAT image is a satellite derived product that allows the orbiting satellites to estimate the current surface wind speeds and directions…sort of like a really long range police radar. It can detect the speed and direction the clouds are moving. Cool stuff that is great during tropical season.

(Image 1 & 2: Visible Satellite/GOES Floater & QUIKSCAT - Courtesy NOAA)

The low, about 130 miles southeast of Charleston, is moving slowly parallel to the coastline. There is a chance that this low could slowly develop over the next few days. The main issue is right now how small it is. Smaller circulations have a more difficult time developing quickly than larger tropical lows. This low is also a “hybrid” low. It has to totally detach itself from the old front so it can become fully “warm core” and complete its tropical transition. There is very little chance of this posing a problem for us but it is something that we will watch closely as it moves northeast. A stronger trough of low pressure should move off the coast on Monday and help push it further away from us and whisk it off to the northeast. Needless to say, some of the forecast models do show this becoming a tropical depression by Tuesday. We will watch it closely for you.

New INVEST - 94L could threaten the Lesser Antilles:
A new tropical disturbance has developed over the far southwestern Atlantic between the Cape Verde islands and the Leeward Islands. The National Hurricane Center (NHC) has designated this area 94L, meaning that they will begin more close monitoring and forecasting of the disturbance. The area of circulation associated with 94L is very large and embedded within some deep tropical moisture, so all indications point to this area developing. All the tropical forecast models do bring 94L to depression strength by the middle of the week but differ in long term tracks.

(Image Courtesy: Colorado State University)

You can see on the initial forecast plots above, if 94L does develop it may very well impact the Lesser Antilles by the weekend.  Some of the more global models say that Bertha will pull 94L north of the islands while some do not develop it at all. We do anticipate that this will become a depression or Tropical Storm later this week. We will continue to watch the forecast guidance daily as it comes in. Too early to tell if it could eventually head toward the United States.

Bertha Hangs On: 

The latest visible picture of Bertha shows that the downgraded hurricane is now a Tropical Storm. The winds have fallen to around 65mph but the storm still has a very impressive circulation and still look somewhat healthy on all the data from satellite reconnaissance.  The U.S. Air Force Hurricane Hunters will investigate the storm later to day to get a better idea on the structure of Bertha. She has not been moving much over the last day or so and that has allowed the surface winds to churn up colder water under the center, which is called upwelling. This is slowly robbing Bertha of the fuel that she needs to keep going. Recent data does show a new slow movement to the northwest and if Bertha can get back over warmer water, she may very well re-gain some strength. As for Bermuda, a Tropical Storm Warning is in effect for the island and the outer bands are visible on radar from the Bermuda Weather Service.

(Image Courtesy: Bermuda Weather Service - Radar)

Bertha will gain the title of the longest lasting tropical cyclone in July (12 days) if it can hold on through Tuesday, which it will. All the forecast guidance agrees that Bertha passes very near Bermuda then is swept northeast over the cooler North Atlantic by the end of next week.

We will watch our coastal waters closely….stay with this week!

Chad Watson
Live 5 Meteorologist

Take a look at the latest visible image of Hurricane Bertha. A well developed eye is visible on the pic below. Its amazing what we can tell about storms today from space, more than 22,000 miles up!

(Image courtesy: Weather Underground)

Looking at some of the latest microwave data from space shows Bertha a good batch of very heavy storms and rain to the north of the center. A nearly closed eyewall is also visible on the picture below. We use these microwave images to basically give us an X-Ray of the storm, much like you see at the hospital. We can derive from the data the current winds and direction, where the heaviest rain is and see the eyewall in action, a great indicator of the storms strength and overall health.

(Image courtesy: Univ. of Wisconsin / CIMSS)

The latest tasking from the National Hurricane Center has the Hurricane Hunters on the way to visit Bertha on Tuesday:

NOUS42 KNHC 061715 AMD
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1000 AM EDT SUN 06 JULY 2008
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
         VALID 07/1100Z TO 08/1100Z JULY 2008
         TCPOD NUMBER.....08-036

I.  ATLANTIC REQUIREMENTS
    1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
    2. SUCCEEDING DAY OUTLOOK. (AMENDED)
       A. POSSIBLE AIR FORCE FLIGHT ON TS BERTHA,
          8/18Z, 20N 57W.
    3.  BEGIN 12 HRLY FIXES 9/12Z IF NECESSARY.

 Chad Watson
Live 5 Meteorologist

Our first hurricane of the 2008 season is here and it’s Bertha. Our tropical storm finally had winds top out at 75mph this morning so the National Hurricane Center pushed Bertha to Hurricane status. The big questions now again surround how strong does she get and where does she go. We have watched the forecast guidance closely over the weekend and I like what I have seen recently…a turn to the right in the long range forecast path. Whats good news for the east coast of the U.S. might be bad news for Bermuda as the storm could pass very near that island.

(Image courtesy: Weather Underground) Infrared Satellite Picture

Infrared and microwave imagery from overnight satellite scans have shown on and off signs that Bertha has a fairly well developed eye feature, roughly 15 miles wide. So far, Bertha has strengethed overall as expected. The storm has been moving over an area of increasing oceanic heat content and will continue to move toward warmer waters in the days ahead. Shear over the storm has stayed at roughly 10-15 knots, which has not really affected the storm as it has tried to become better organized. Intensity guidance maintains Bertha as a hurricane over the next 5 days.

(Image courtesy: Weather Underground) Tropical Forecast Model Plots

So…where does she go. All bets right now are on a northward turn somewhere in the 4-5 day range over the west-central Atlantic. The big issue is when that turn starts to happen. It all is based on a weakness in the Bermuda High forecast by some of the global forecast models. The stronger the storm is, the more impact the weakness might have on Bertha, turning it north sooner. If the weakness is not as strong as forecast, Bertha may continue on a more northwesterly course, not turning until it is west of Bermuda. Then comes the out lier…some of our guidance says that Bertha may not turn at all. So as you can see, there is very little confidence in the long term track. Is it a threat to the U.S.? Right now, I say not likely, but its all dependent on that northward turn. If Bertha was to affect the coast, it would come in 6-8 days.

It is interesting to note that on this day, July 7th 1993…another Hurricane Bertha formed in the Atlantic Ocean. That Bertha did make it all the way to the U.S. coast and brushed the South Carolina coast before making landfall in North Carolina near the Outer Banks.

We will continue to watch Bertha and have the latest here on the Blog and over in the Hurricane Center.

Chad Watson
Live 5 Meteorologist