1. Showers and thunderstorms have increased this morning in association
with an area of low pressure located several hundred miles southwest
of the coast of Mexico. Environmental conditions are forecast to be
conducive for some gradual development, and a tropical depression is
likely to form late this weekend or early next week as the system
moves slowly toward the west-northwest away from the coast of
Mexico.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 5 days...high...70 percent.
Tropical Storm Polo Discussion Number 4
NWS National Hurricane Center Miami FL EP212020
700 AM PST Wed Nov 18 2020
Satellite images indicate that the depression has strengthened into
a tropical storm. The small central dense overcast has grown
during the past several hours and a few banding features have
formed. Dvorak estimates range from 30 to 45 kt, and the initial
wind speed is set to 40 kt, which matches the latest CIMSS
satellite consensus estimate. Polo could strengthen a little more
today, but an increase in shear and dry-air entrainment should
start the weakening process on Thursday, with the system expected
to become a non-convective remnant low on Friday. The new NHC
forecast is a little below the model consensus, close to the
previous NHC forecast, leaning toward the idea that the small
tropical cyclone will probably weaken faster than the bulk of the
guidance anticipates.
The initial motion continues to be west-northwestward at 10 kt.
There has been no change to the forecast philosophy, with Polo
forecast to remain on the southern side of a mid-level ridge
throughout the period. The storm should turn more westward on
Thursday as the system weakens and becomes more shallow. The new
forecast is south of the latest model consensus, nudged slightly
north of the previous NHC forecast.
Tropical Depression Twenty-One-E Discussion Number 1
NWS National Hurricane Center Miami FL EP212020
300 PM MDT Tue Nov 17 2020
Visible satellite imagery and recent ASCAT data indicate that the
circulation of the area of low pressure located well south-southwest
of Baja California has become better defined today. The associated
convective activity has also become organized in a band around the
western and southwestern portions of the circulation. Therefore,
the system is being classified as a tropical depression with winds
of 30 kt, as indicated by the scatterometer data and a T2.0 (30 kt)
Dvorak classification from TAFB.
The depression is currently located over SSTs of around 28 deg C,
and within a low shear environment. These conditions are conducive
for strengthening, but the surrounding mid-level environment is
fairly dry which is likely to limit intensification. Most of the
intensity guidance calls for the system to become a short-lived
tropical storm, and so does the official forecast. After 24 hours,
increasing upper-level westerly winds, cooler SSTs, and even less
favorable thermodynamic conditions should cause the cyclone to
weaken. The system is likely to become a remnant low in about 48
hours, and the global models show it degenerating into a trough of
low pressure in 60-72 hours, which is also indicated in the NHC
forecast.
The initial motion estimate is 285/11 kt. A mid-level ridge that
extends westward from northern Mexico over the eastern Pacific
should steer the system west-northwestward for the next couple of
days. After that time, the cyclone is likely to turn more westward
as it weakens and is steered by the low-level trade wind flow. The
track guidance is in good agreement, and the NHC forecast is near
the middle of the guidance envelope.
1. Visible satellite imagery indicates that the circulation of the
area of low pressure located several hundred miles south-southwest
of the southern tip of the Baja California peninsula has become
better defined, and the associated shower and thunderstorm
activity is also showing signs of organization. Although
environmental conditions are only somewhat conducive for additional
development, only a slight increase in organization of the system
would result in the formation of a short-lived tropical depression
late today or tomorrow as it moves west-northwestward or
northwestward at about 10 mph. Conditions are forecast to become
increasingly unfavorable for further development on Thursday.
* Formation chance through 48 hours...high...70 percent.
* Formation chance through 5 days...high...70 percent.
WTPN21 PHNC 171530
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT (INVEST 98E)//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
160 NM EITHER SIDE OF A LINE FROM 14.3N 110.8W TO 15.9N 118.1W
WITHIN THE NEXT 06 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS
IN THE AREA ARE ESTIMATED TO BE 20 TO 25 KNOTS. METSAT IMAGERY AT
171500Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 14.4N
111.4W. THE SYSTEM IS MOVING WESTWARD AT 10 KNOTS.
2. REMARKS: AN AREA OF CONVECTION (INVEST 98E) HAS PERSISTED NEAR
14.4N 111.4W, APPROXIMATELY 257NM SOUTH OF SOCORRO, MEXICO. ANIMATED
ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM
WITH PERSISTENT DEEP CONVECTION AND FORMATIVE BANDING. A 171143Z
SSMIS 37GHZ MICROWAVE IMAGE DEPICTS CURVED CONVECTIVE BANDING
WRAPPING TIGHTLY INTO A RAGGED BUT DEFINED LOW-LEVEL CIRCULATION
CENTER. UPPER-LEVEL ANALYSIS REVEALS A MARGINALLY-FAVORABLE
ENVIRONMENT WITH LOW VERTICAL WIND SHEAR AND FAIR POLEWARD OUTFLOW.
SST VALUES OF 28C ARE CONDUCIVE FOR FURTHER DEVELOPMENT. GLOBAL
MODELS INDICATE A WEST-NORTHWESTWARD TRACK OVER THE NEXT 1-2 DAYS
WITH LIMITED DEVELOPMENT. MAXIMUM SUSTAINED SURFACE WINDS ARE
ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED
TO BE NEAR 1004 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A
SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS HIGH.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY
181530Z.//
NNNN
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