Aug 1, 2014

Tropical Storm Bertha forms to the east-southeast of Barbados

IR satellite picture of Trop. Storm Bertha

 An area of convection as flared up to the north and northeast of the low pressure circulation over the Atlantic Ocean located to the ESE of the Lesser Antilles. The organization of the system now warrants classification of the disturbance as a tropical storm - in this case  Tropical Storm Bertha. The NHC is now issuing advisories on this system
The storm is moving toward the WNW at 20 mph with maximum winds of near 40 mph. Environmental conditions currently around the storm's circulation and along its forecast path only favor marginal intensification.
Latest position/strength of TS BERTHA

"Spaghetti" model plots
The "spaghetti plots are tightly clustered on WNW track and the official NHC track is pretty much in agreement. Due to the expect WNW track at a rather brisk forward speed Watches and Warnings have been posted for parts of the Lesser Antilles and also across some islands in the Greater Antilles chain.
Official NHC forecast track for Bertha

Tropical Warnings/Watches currently in effect
A TROPICAL STORM WARNING is in effect for:
* Barbados * St. Lucia  * Dominica 
A TROPICAL STORM WATCH is in effect for:
* Puerto Rico * Vieques  * Culebra * U.S. Virgin Islands
* St. Vincent and The Grenadines

Jul 31, 2014

Potpourri Weather Post

Don't be surprised by today's storms

KENX radar
There could be a few thunderstorms today and they might be locally strong or marginally severe. Main threats for today: hail 1/2" to perhaps 1" in diameter, winds gusting 40-50mph, heavy rain and of course DANGEROUS cloud to ground lightning. One small line of storms is moving out of Eastern NY State (with a warning out for Washington and Saratoga counties in NY) to Bennington county in VT. More scattered cells are "popping" up farther to the west.  

31 July 12z Albany, NY Rawindsonde 
The reason for only a marginal threat 
of severe weather for today is that  CAPE (potential instability) is small, wind shear is moderate and lapse rates are weak as indicated by the morning "sounding" from Albany NY (which I modified for the expected maximum temperature and dew point for today [at the surface]). 

CHAP/RI computations for 31 July 2014 for Eastern NY State
Using the data I then "ran" the Convective Hazard Assessment Program or CHAP (also know as Ricks' Index or RI)  to gauge the probability of severe weather. An RI value of < 110 implies NO SEVERE thunderstorms while a value of 160 implies SEVERE thunderstorms are likely. The RI can also be useful in predicting potential hail size, maximum wind from the storms, radar VIL [storms that reach or exceed this value of the VIL could be severe] and rainfall. Today's RI = 116 so hail size could be around 1/2 or so, winds could gust to 40-45 mph. The Probability of Precipitation (PoP) for today is 40% with the Probability of Severe storms (PoSVR) is only 7%. Rainfall of around 8/10 ( 0.80") is possible in storms with MAXIMUM potential rainfall of 2". Storms will tend to move quickly towards the ENE at 30-35 mph, so I would think that the threat for any flash flooding from today's storms is LOW.

Atlantic Tropical Disturbance to the southeast of the Leeward Islands

From the National Hurricane Center
200 PM EDT THU JUL 31 2014

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

1. A Hurricane Hunter aircraft has recently begun investigating the
low pressure system located about 550 miles east of the southern
Windward Islands.  Preliminary reports from the aircraft indicate
that this system is producing winds to near gale force.  However,
satellite images indicate that the associated showers and
thunderstorms have diminished significantly since this morning.
Therefore the low currently does not meet the criteria to designate
it as a tropical cyclone.  Showers and thunderstorms could
redevelop later today or tonight, which could result in tropical
cyclone formation.  Interests in the Lesser Antilles should continue
to monitor the progress of this disturbance as it moves
west-northwestward at 15 to 20 mph, and watches or warnings may be
required for some of these islands later today or tonight.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...70 percent.

Forecaster Pasch

Visible Satellite picture of tropical disturbance 93L

Model forecast tracks for tropical disturbance 93L