TROPICAL STORM NORA DISCUSSION NUMBER 8
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP182015
1100 PM HST SAT OCT 10 2015
DEEP CONVECTION HAS INCREASED NEAR THE CENTER OF NORA DURING THE
PAST SEVERAL HOURS. DVORAK CURRENT INTENSITY ESTIMATES RANGED FROM
3.5/55 KT FROM HFO TO 2.5/35 KT FROM SAB...WHILE CIMSS ADT CAME IN
AT 51 KT. GIVEN THE IMPROVEMENT IN THE SATELLITE PRESENTATION...A
BLEND OF THESE INPUTS SUPPORTS RAISING THE INITIAL INTENSITY TO 50
KT.
SLOW INTENSIFICATION IS LIKELY DURING THE NEXT COUPLE OF DAYS...
FOLLOWED BY WEAKENING ON DAYS 3 THROUGH 5. AN UPPER LEVEL
ANTICYCLONE TO THE NORTHEAST OF NORA AND A WEAK UPPER LEVEL TROUGH
TO THE NORTHWEST ARE CREATING AN OUTFLOW CHANNEL TO THE
NORTHWEST...THOUGH SOUTHERLY WINDS ALOFT ARE INHIBITING OUTFLOW
ELSEWHERE AND PRODUCING VERTICAL WIND SHEAR OF AROUND 10 KT
ACCORDING TO SHIPS AND THE LATEST CIMSS ANALYSIS. THESE WINDS ALOFT
ARE EXPECTED TO DIMINISH DURING THE NEXT 24 HOURS AS THE UPPER
LEVEL TROUGH BRIEFLY RETREATS...AND THE SEA SURFACE TEMPERATURE
WILL REMAIN AROUND 29C ALONG THE FORECAST TRACK IN THE SHORT TERM.
AS A RESULT...SLOW INTENSIFICATION IS EXPECTED DURING THE NEXT
COUPLE OF DAYS. WEAKENING IS FORECAST TO BEGIN LATE MONDAY OR
TUESDAY AS A DEEP TROUGH DEVELOPING OVER HAWAII IMPARTS INCREASING
VERTICAL WIND SHEAR. THE INTENSITY FORECAST WAS CHANGED LITTLE FROM
THE PRIOR ADVISORY AND CLOSELY FOLLOWS THE TRENDS OF SHIPS AND ICON
WHILE PEAKING THE INTENSITY OF NORA SLIGHTLY HIGHER THAN THESE
GUIDANCE MEMBERS.
NORA CONTINUES TO MOVE WESTWARD...280 DEGREES...AT 11 KT. THIS
GENERAL MOTION IS EXPECTED TO CONTINUE INTO MONDAY AS NORA IS
STEERED BY A DEEP RIDGE CENTERED SEVERAL HUNDRED MILES TO THE
NORTH. A TURN TOWARD THE NORTHWEST IS EXPECTED TO OCCUR LATE MONDAY
AND TUESDAY AS THE DEEP TROUGH DEVELOPING OVER HAWAII CREATES A
WEAKNESS IN THE RIDGE TO THE NORTH OF NORA. NORA IS EXPECTED TO TURN
NORTH THEN EVENTUALLY NORTHEAST ON DAYS 3 THROUGH 5 AS THE SYSTEM
INCREASINGLY INTERACTS WITH THE TROUGH. WHILE THERE IS SOME
UNCERTAINTY AND MODEL SPREAD REGARDING THE EXACT TIMING OF THE
TURN...IT IS EXPECTED TO OCCUR SEVERAL HUNDRED MILES SOUTHEAST OF
HAWAII. THE FORECAST WAS SHIFTED SLIGHTLY WESTWARD FROM 48 HOURS AND
BEYOND AND IS CLOSE TO THE GFEX AND TVCN.
TROPICAL STORM NORA DISCUSSION NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL EP182015
800 PM PDT FRI OCT 09 2015
Deep convection has increased a little since the last advisory,
with the center located on the southeastern edge of the convective
mass due to light/moderate southeasterly shear over the cyclone.
The initial intensity is set to 35 kt based on the latest Dvorak
classifications from TAFB and SAB, marking the formation of
Tropical Storm Nora, the 14th tropical storm of the eastern North
Pacific season. Environmental conditions appear favorable for
continued steady strengthening for the next 72 hours, with the
cyclone moving over SSTs at or above 29C during that period and
light shear. By days 4 and 5 the SHIPS model and global model fields
show the shear increasing, which should result in weakening. The
new NHC forecast is largely an update of the previous one, and is
close to or a little above the SHIPS model through the period.
The initial motion estimate is 275/14, as Nora is being steered
quickly westward by a subtropical ridge to the north. A gradual
decrease in forward speed is forecast during the next 36 hours as
the ridge slowly weakens, and Nora should then turn west-
northwestward as a weakness develops around 145W. Nora is then
forecast to recurve between a deep-layer trough over the north-
central Pacific and a strengthening ridge to the southeast by the
end of the period. The track model guidance is in overall good
agreement on this scenario, and the new NHC forecast is close to a
blend of the GFS and ECMWF models through the period. The new
official forecast is a little north of the previous one through 48
hours, and then is a little to the left, showing a more gradual
recurvature following the latest trend in the guidance.
TROPICAL DEPRESSION EIGHTEEN-E DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL EP182015
800 AM PDT FRI OCT 09 2015
Satellite images indicate that the area of low pressure in the far
southwestern portion of the eastern Pacific has become better
organized. Curved banding features have increased, along with a
growing area of deep convection near the center. Thus the system
is declared a tropical depression, the 18th of the season. The
initial wind speed is set to 30 kt using the Dvorak estimate
from TAFB. The minimum pressure is 1008 mb on the basis of buoy
43535 near the depression, which reported 1009 mb a couple of hours
ago.
The cyclone is expected to be in a favorable environment for
strengthening for the next few days, with low wind shear, very warm
waters and high mid-level moisture. Thus steady intensification is
forecast until early next week. Thereafter, an increase in
southwesterly shear and some cooler waters should cause the cyclone
to weaken some by day 5. The official intensity prediction is on
the high side of the intensity guidance, a reflection of both the
conducive environment and the low bias of the guidance during this
season. It would not be surprising if the cyclone intensified more
than shown here given the large-scale environment, but timing this
is not possible at this time.
The depression is moving westward at about 12 kt. This general
motion is expected for the next 2-3 days while it remains under the
influence of the subtropical ridge located over the eastern and
central Pacific. This pattern is expected to change quickly after
day 3 when a mid-latitude trough erodes the ridge, causing the
cyclone to recurve well east of the Hawaiian Islands. For a first
forecast, the guidance is in rather good agreement, and the
official forecast is close to the overall consensus, with a bit more
weight on the ECMWF model.
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