WTPZ42 KNHC 060250 RRA

TCDEP2



TROPICAL STORM JOHN DISCUSSION NUMBER   2

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP122018

900 PM MDT SUN AUG 05 2018



CONVECTION ASSOCIATED WITH TROPICAL DEPRESSION TWELVE-E HAS

CONTINUED TO BECOME BETTER ORGANIZED, ALTHOUGH RECENT MICROWAVE

SATELLITE DATA SUGGEST THE LOW-LEVEL CENTER IS ELONGATED FROM

NORTHWEST TO SOUTHEAST.  SATELLITE INTENSITY ESTIMATES FROM TAFB AND

SAB HAVE INCREASED TO 35 KT, AND BASED ON THESE THE DEPRESSION IS

UPGRADED TO TROPICAL STORM JOHN.



THE INITIAL MOTION IS 315/7.  A WESTWARD-MOVING MID- TO UPPER-LEVEL

TROUGH OVER NORTHERN MEXICO HAS WEAKENED THE SUBTROPICAL RIDGE OVER

THE NORTHEASTERN PACIFIC, AND THE LARGE-SCALE MODELS ARE IN GOOD

AGREEMENT THAT JOHN WILL MOVE NORTHWESTWARD AT AN INCREASING

FORWARD SPEED TOWARD THIS WEAKNESS.  A COMPLICATING FACTOR IS THAT

JOHN MAY INTERACT WITH TROPICAL STORM ILEANA TO THE EAST.  HOWEVER,

JOHN IS MUCH LARGER THAN ILEANA, AND THE MOST LIKELY IMPACT OF THIS

INTERACTION IS THAT JOHN COULD MOVE A LITTLE SLOWER THAN CURRENTLY

FORECAST.  THE NEW FORECAST TRACK IS A LITTLE TO THE NORTH OF THE

PREVIOUS TRACK AFTER 48 H, BUT IS OTHERWISE SIMILAR TO THE PREVIOUS

FORECAST.  THE NEW TRACK ALSO LIES JUST SOUTH OF THE CLUSTER OF

CONSENSUS MODELS.



JOHN IS EXPECTED TO BE IN AN ENVIRONMENT OF VERY WARM SSTS, LOW

SHEAR, AND A MOIST ATMOSPHERE THROUGH ABOUT 60 H.  THIS ENVIRONMENT

IS QUITE FAVORABLE FOR RAPID INTENSIFICATION (RI), AS INDICATED BY

HIGH PROBABILITIES IN THE SHIPS RI INDEX, AND IT IS LIKELY THAT RI

WILL BEGIN AS SOON AS THE INNER CORE OF THE STORM BECOMES BETTER

ORGANIZED.  THE NHC FORECAST CALLS FOR THE STORM TO BECOME A