WTNT42 KNHC 171452 RRA

TCDAT2



TROPICAL STORM KARL DISCUSSION NUMBER  13

NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122016

1100 AM AST SAT SEP 17 2016



KARL HAS BEEN IN A FAIRLY STEADY STATE DURING THE PAST DAY OR MORE

WITH CONVECTION PERIODICALLY FIRING NEAR THE CENTER AND A LARGER

AREA OF MORE CONTINUOUS THUNDERSTORMS FAR FROM THE CENTER.  SHIP

BATFR18 REPORTED SUSTAINED WINDS OF ABOUT 40 KT AT 1100 UTC, WHICH

SUPPORT KEEPING THAT WIND SPEED FOR THIS ADVISORY.  THE SHEAR THAT

HAS BEEN AFFECTING KARL SHOULD GRADUALLY DIMINISH OVER THE NEXT

COUPLE OF DAYS AS IT MOVES AWAY FROM A NEARBY UPPER-LEVEL LOW.  A

SMALL AMOUNT OF WEAKENING IS POSSIBLE IN THE SHORT TERM SINCE THE

SYSTEM IS STILL STRUGGLING AGAINST THE SHEAR. THEREAFTER,

STRENGTHENING IS ANTICIPATED DUE TO KARL LIKELY MOVING OVER

VERY WARM WATERS CONCURRENT WITH RATHER LIGHT SHEAR. ONE QUESTION

MARK IS THE AMOUNT OF AVAILABLE MOISTURE IN THE MID-LEVELS, WITH

BOTH THE ECMWF AND THE GFS SHOWING A SOMEWHAT DRY ENVIRONMENT. WHILE

A LOT OF THE TROPICAL-CYCLONE-SPECIFIC INTENSITY GUIDANCE SHOWS A

HURRICANE AT LONG RANGE, THE MARGINAL MOISTURE ENVIRONMENT FORECAST

BY THOSE TWO GLOBAL MODELS MAKES ME THINK TWICE ABOUT GOING TOO

HIGH.  THE NEW FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE AND IS

SIMILAR TO A BLEND OF THE SHIPS/LGEM MODELS.



KARL HAS BEEN WOBBLING A LITTLE SOUTH OF DUE WEST DURING THE DAY,

DEPENDING ON HOW MUCH CONVECTION IS NEAR THE CENTER. A STRENGTHENING

LOW- TO MID-LEVEL RIDGE OVER THE CENTRAL ATLANTIC IS EXPECTED TO

CONTINUE PUSHING KARL SOUTH OF DUE WEST DURING THE NEXT 24 HOURS.

AFTER THAT TIME, KARL SHOULD MOVE MORE TO THE WEST-NORTHWEST AROUND=