Cloud Stalker: Hurricane Bertha

Thursday, July 10, 2008

Hurricane Bertha

Hurricane Bertha is back at Category 2 status, and appears destined to become one of the longest-lasting July hurricanes on record. Hurricane Emily of 2005 spent seven full days at hurricane strength in July, which I believe is the record. Bertha is halfway there. The storm is in no hurry to recurve out to sea, and will spend 3-4 more days over waters warm enough to maintain it at hurricane intensity.
She sure has been fun to watch, I can honestly say. She is no threat to anyone yet, but Bermuda needs to keep an eyes this storm.

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
500 PM AST THU JUL 10 2008

...BERTHA STILL A NORTHWESTWARD-MOVING CATEGORY ONE HURRICANE...

IT IS STILL TOO EARLY TO DETERMINE THE EXTENT TO WHICH BERTHA COULD
IMPACT BERMUDA. INTERESTS ON THAT ISLAND SHOULD CLOSELY MONITOR
THE PROGRESS OF BERTHA DURING THE NEXT SEVERAL DAYS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED
BY YOUR LOCAL WEATHER OFFICE.

AT 500 PM AST...2100Z...THE CENTER OF HURRICANE BERTHA WAS LOCATED
NEAR LATITUDE 27.2 NORTH...LONGITUDE 60.8 WEST OR ABOUT 425 MILES...
685 KM...SOUTHEAST OF BERMUDA.

BERTHA IS MOVING TOWARD THE NORTHWEST NEAR 10 MPH...17 KM/HR. A
TURN TOWARD THE NORTH AND A DECREASE IN FORWARD SPEED ARE EXPECTED
DURING THE NEXT 48 HOURS. ON THE FORECAST TRACK...BERTHA WILL
SLOWLY APPROACH BERMUDA FRIDAY AND SATURDAY.

MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 85 MPH...
140 KM/HR...WITH HIGHER GUSTS. BERTHA IS A CATEGORY ONE HURRICANE
ON THE SAFFIR-SIMPSON SCALE. SOME FLUCTUATIONS IN STRENGTH ARE
POSSIBLE DURING THE NEXT 48 HOURS.

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 HAVE STARTED TO AFFECTED BERMUDA. THESE
CONDITIONS ARE EXPECTED TO PERSIST FOR THE NEXT FEW DAYS.

REPEATING THE 500 PM AST POSITION...27.2 N...60.8 W. MOVEMENT
TOWARD...NORTHWEST NEAR 10 MPH. MAXIMUM SUSTAINED WINDS...85 MPH.
MINIMUM CENTRAL PRESSURE...980 MB.

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.