WTPZ44 KNHC 310848 RRA

TCDEP4



TROPICAL STORM LIDIA DISCUSSION NUMBER   7

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP142017

300 AM MDT THU AUG 31 2017



SCATTEROMETER DATA AND MICROWAVE IMAGES INDICATE THAT LIDIA HAS A

DEFORMED CIRCULATION, WITH WHAT APPEARS TO BE TWO LOBES OF

VORTICITY ROTATING AROUND A COMMON CENTER.  THE UNMANNED NASA GLOBAL

HAWK FLEW VERY NEAR THE CENTROID OF THE CIRCULATION LAST EVENING

AND PROVIDED A BETTER ESTIMATE OF LIDIA'S CENTRAL PRESSURE (ABOUT

998 MB AT THE TIME).  IN ADDITION, A DROPSONDE RELEASED TO THE EAST

OF THE CENTER MEASURED A MEAN BOUNDARY LAYER WIND OF 45 KT, WHICH

EQUATES TO A SURFACE WIND A LITTLE OVER 35 KT.  ASSUMING THE

DROPSONDE DID NOT SAMPLE THE HIGHEST WINDS, AND GIVEN THAT DEEP

CONVECTION HAS BECOME MORE ORGANIZED INTO TWO DISTINCT CLUSTERS

SINCE THAT TIME, THE INITIAL INTENSITY IS RAISED TO 40 KT.



LIDIA IS MOVING NORTH-NORTHWESTWARD, OR 335/7 KT, BETWEEN A

MID-LEVEL HIGH CENTERED OVER CENTRAL MEXICO AND A CYCLONIC GYRE

LOCATED TO THE WEST OVER THE PACIFIC.  THIS MOTION SHOULD CONTINUE

FOR THE NEXT 36 HOURS, BUT THEN AFTER THAT TIME, HIGH PRESSURE OVER

THE SOUTHWESTERN UNITED STATES SHOULD FORCE LIDIA TO TURN

NORTHWESTWARD AND WEST-NORTHWESTWARD ON DAYS 2 THROUGH 5.  MOST OF

THE SPREAD IN THE TRACK MODELS IS RELATED TO LIDIA'S FORWARD SPEED,

AND THERE IS A NOTABLE DISPARITY BETWEEN THE FASTER GFS AND SLOWER

ECMWF MODELS.  THE NEW NHC TRACK FORECAST IS A LITTLE FASTER THAN

THE PREVIOUS ONE TO BETTER MATCH THE SPEEDS OF THE TVCN MULTI-MODEL

CONSENSUS AND THE HFIP CORRECTED CONSENSUS APPROACH (HCCA).



EVEN THOUGH LIDIA IS IN AN ENVIRONMENT OF LOW SHEAR AND OVER VERY