Cloud Stalker: Hurricane Bertha

Friday, July 11, 2008

Hurricane Bertha

Hurricane Bertha continues trundling along towards Bermuda, but is not in a hurry to get there. The storm has a rather sloppy appearance on satellite loops, thanks to the fact that the eyewall dissolved last night, with a new, much larger eye taking its place. Bertha will probably start to intensify today now that this Eyewall Replacement Cycle (ERC) is done. Wind shear is low (less than 10 knots) and water temperatures are warm (28°C). Shear if forecast to remain below 10 knots until Sunday, but the water temperatures will gradually cool to 26°C by the time Bertha reaches Bermuda's latitude on Sunday. Intensification back to Category 2 status seems probable, and Bertha still has an outside chance at reaching Category 3 status again. The Air Force Hurricane Hunters will make their first flight into Bertha this afternoon to check on the storm's strength.

AT 1100 AM AST...1500Z...THE CENTER OF HURRICANE BERTHA WAS LOCATED
NEAR LATITUDE 28.5 NORTH...LONGITUDE 62.0 WEST OR ABOUT 310 MILES...
500 KM...SOUTH-SOUTHEAST OF BERMUDA.

BERTHA IS MOVING TOWARD THE NORTHWEST NEAR 6 MPH...9 KM/HR.
THIS GENERAL MOTION IS EXPECTED TO CONTINUE TODAY WITH A GRADUAL
TURN TO THE NORTH DURING THE NEXT 24 HOURS. ON THIS TRACK...
BERTHA'S FRINGES WILL BE NEARING BERMUDA ON SATURDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 85 MPH...140 KM/HR...WITH HIGHER
GUSTS. BERTHA IS A CATEGORY ONE HURRICANE ON THE SAFFIR-SIMPSON
SCALE. SOME FLUCTUATIONS IN INTENSITY ARE POSSIBLE DURING THE NEXT
24 HOURS. AN AIR FORCE RESERVE RECONNAISSANCE AIRPLANE IS SCHEDULED
TO CHECK BERTHA LATER TODAY.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 30 MILES...45 KM...FROM
THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 140
MILES...220 KM.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 980 MB...28.94 INCHES.

LARGE SWELLS AND HIGH SURF ARE AFFECTING BERMUDA...AND THESE
CONDITIONS ARE EXPECTED TO PERSIST FOR THE NEXT FEW DAYS.

REPEATING THE 1100 AM AST POSITION...28.5 N...62.0 W. MOVEMENT
TOWARD...NORTHWEST NEAR 6 MPH. MAXIMUM SUSTAINED WINDS...85 MPH.
MINIMUM CENTRAL PRESSURE...980 MB.

AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 200 PM AST FOLLOWED BY THE NEXT COMPLETE ADVISORY AT 500
PM AST.

Jess
Cloud Stalker

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HAIL (3/4 inch or greater)

Hail can cause significant damage to your vehicle, break windows and damage roofs of homes and businesses.
Hail can cause significant bodily injuries such as broken bones and even blindness if wind blown.
Softball (4.5 inches) sized hail was reported in Lake Wales, Florida on March 30, 1996.
Haildrifts, up to four feet deep of dime to nickel sized hail, occurred in low-lying areas near Zephyrhills, Florida on January 29, 1997.
Hailstones the size of softballs can fall at speeds faster than 100 mph

supercell

Supercells derive their rotation through tilting of horizontal vorticity (an invisible horizontal vortex) caused by wind shear. Strong updrafts lift the air turning about a horizontal axis and cause this air to turn about a vertical axis. This forms the deep rotating updraft, the mesocyclone.
A cap or capping inversion is usually required to form a downdraft of sufficient strength. The cap puts an inverted (warm-above-cold) layer above a normal (cold-above-warm) boundary layer, and by preventing warm surface air from sinking too far, allows one or both of the following:
Air below the cap warms and/or becomes more moist
Air above the cap cools
This creates a warmer, moister layer below a cooler layer, which is increasingly unstable (because warm air is less dense and tends to rise). When the cap weakens or moves, explosive development follows.
In North America, supercells usually show up on Doppler radar as starting at a point or hook shape on the southwestern side, fanning out to the northeast. The heaviest precipitation is usually on the southwest side, ending abruptly short of the rain-free updraft base or main updraft (not visible to radar). The rear flank downdraft, or RFD, carries precipitation counterclockwise around the north and northwest side of the updraft base, producing a "hook echo" that indicates the presence of a mesocyclone.