WTPZ42 KNHC 142033 RRA

TCDEP2



TROPICAL STORM NORMA DISCUSSION NUMBER   2

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172017

300 PM MDT THU SEP 14 2017



NORMA HAS A BROAD AND WELL-DEFINED CIRCULATION WITH MULTIPLE

CONVECTIVE BANDS, ESPECIALLY TO THE EAST AND SOUTH OF THE CENTER.

ALTHOUGH THE CONVECTIVE BANDS ARE A LITTLE BROKEN IN INFRARED

IMAGERY, DVORAK INTENSITY ESTIMATES HAVE GONE UP TO T3.5 FROM TAFB

AND T2.5 FROM SAB AND CIMSS AT THE UNIVERSITY OF WISCONSIN.  THE

INITIAL INTENSITY HAS THEREFORE BEEN RAISED TO 40 KT.



THE CYCLONE CONTINUES TO MOVE SLOWLY NORTHWARD WITH AN INITIAL

MOTION OF 010/5 KT.  AS MENTIONED IN THE PREVIOUS DISCUSSION, A

BLOCKING HIGH TO THE NORTH OF NORMA SHOULD IMPEDE ITS NORTHWARD

MOTION FOR THE NEXT 48 HOURS, WITH THE FORWARD SPEED STAYING BELOW

5 KT.  THERE IS STILL NO CLARITY ON THE FORECAST TRACK AFTER 48

HOURS, WITH THE NEW 12Z ECMWF AND UKMET MODELS REMAINING ON THE

WESTERN SIDE OF THE GUIDANCE ENVELOPE TO THE WEST OF THE BAJA

CALIFORNIA PENINSULA, WHILE THE REMAINDER OF THE MODELS GENERALLY

SHOW A TRACK OVER THE SOUTHERN PART OF THE PENINSULA THEN TURNING

INTO NORTHWESTERN MEXICO.  SINCE THE TRACKS OF THE GFS AND HWRF

MODELS LIE CLOSE TO THE TVCN MULTI-MODEL CONSENSUS AND HCCA, THE

NHC OFFICIAL FORECAST CONTINUES TO FAVOR THIS SET OF MODELS.

STILL, CONFIDENCE IN THE FORECAST AFTER 48 HOURS IS QUITE LOW AT

THIS TIME.



SINCE NORMA ALREADY HAS A WELL-STRUCTURED CIRCULATION, WARM WATERS

AND LOW SHEAR SHOULD LEAD TO A FAIRLY FAST INCREASE IN INTENSITY

OVER THE NEXT COUPLE OF DAYS.  THE UPDATED NHC INTENSITY FORECAST

IS A LITTLE HIGHER THAN THE PREVIOUS ONE AND IS GENERALLY CLOSE TO