1. An area of disturbed weather extends several hundred miles south of
the coast of southwestern Mexico. A broad area of low pressure is
expected to form from this disturbance in a couple of days, and
gradual development of the low is possible during the early to
middle part of next week while it moves generally west-northwestward
away from the coast of Mexico at 5 to 10 mph.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...medium...40 percent.
1. Showers and thunderstorms associated with a broad area of low
pressure located a couple of hundred miles south-southwest of
Manzanillo, Mexico, are showing signs of organization.
Environmental conditions are forecast to be conducive for additional
development, and a tropical depression is expected to form early
next week while the system moves west-northwestward at about 10 mph,
away from the coast of Mexico.
* Formation chance through 48 hours...medium...60 percent.
* Formation chance through 5 days...high...80 percent.
WTPN21 PHNC 201130
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
145 NM EITHER SIDE OF A LINE FROM 14.9N 106.5W TO 16.8N 111.8W
WITHIN THE NEXT 12 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 200600Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 15.0N 106.8W. THE SYSTEM IS MOVING NORTH-NORTHWESTWARD AT 11
AN AREA OF CONVECTION (INVEST 93E) HAS PERSISTED NEAR 15.0N 106.8W,
APPROXIMATELY 275 NM SOUTHWEST OF MANZANILLO, MEXICO. ANIMATED
ENHANCED INFRARED SATELLITE IMAGERY AND A 200740Z GMI PARTIAL PASS
SHOWS AN AREA OF DEEPENED CONVECTION ASSOCIATED WITH A CONSOLIDATING
LOW LEVEL CIRCULATION CENTER (LLCC). UPPER LEVEL ANALYSIS INDICATES
THE DISTURBANCE IS LOCATED UNDER AN AREA OF WEAK (5-10 KTS) VERTICAL
WIND SHEAR AND EQUATORWARD WIND FLOW. ADDITIONALLY, WARM (29-30
CELSIUS) SEA SURFACE TEMPERATURES ARE CONDUCIVE FOR TROPICAL
TRANSITION. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO
25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1007
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
1. Satellite images indicate that the circulation associated with the
low pressure system centered about 350 miles southwest of
Manzanillo, Mexico, has become better defined today, with
thunderstorm activity still showing signs of organization. If this
trend continues, advisories could be initiated on a tropical
depression later today or tonight, and environmental conditions are
forecast to be conducive for additional development while the system
moves west-northwestward at about 10 mph.
* Formation chance through 48 hours...high...near 100 percent.
* Formation chance through 5 days...high...near 100 percent.
Tropical Depression Seventeen-E Discussion Number 1
NWS National Hurricane Center Miami FL EP172020
300 PM MDT Sun Sep 20 2020
The area of disturbed weather several hundred miles south of the
southern tip of Baja California has developed enough organized deep
convection and a well-enough defined center to declare it a tropical
cyclone. This is supported by subjective Dvorak classifications
from both SAB and TAFB with an initial intensity of 25 kt. The
initial motion is an uncertain 275 degrees at 9 kt.
As the system should be moving over warm 29C SSTs, encountering
moist mid-level humidities, and experiencing low to moderate amounts
of tropospheric vertical shear, steady intensification is expected
through the next three days. Around days four and five, the tropical
cyclone should encounter both drier air and cooler SSTs, likely
curtailing any further development and leading toward slow
weakening. The intensity forecast is between the bullish dynamical
models calling for a peak at a Category 1 hurricane in about three
days, and the bearish statistical guidance suggesting a moderate to
high-end tropical storm at the system's peak.
The track models are in much better agreement with all suggesting a
turn toward the west-northwest at a slightly faster forward speed
for the next three days, under the steering influence of a narrow
deep-layer ridge north of the system. By day four, an amplifying
ridge north of the tropical cyclone should turn it back toward the
west again. The track forecast is based upon the HCCA corrected
Tropical Storm Lowell Discussion Number 5
NWS National Hurricane Center Miami FL EP172020
300 PM MDT Mon Sep 21 2020
Tropical Depression Seventeen-E has continued to have a ragged
appearance in satellite imagery during the day. The circulation is
elongated, with the main center just northeast of a poorly organized
convective mass and a secondary vorticity maximum well to the
north-northeast near Socorro Island. However, recent scatterometer
data showed an area of 35-40 kt winds to the south and southeast of
the main center. Based on this, the depression is upgraded to
Tropical Storm Lowell with an initial intensity of 40 kt.
The initial motion is now 290/14 kt. There are no significant
changes in the track forecast philosophy, the track forecast
guidance, or the track forecast since the last advisory. Lowell is
being steered by a large low- to mid-level ridge to the north and
northwest, and this ridge is forecast to persist through the
forecast period. The track guidance shows that the system should
continue west-northwestward for about 36 h, followed by a westward
motion through 120 h. The track guidance is still very tightly
clustered, and the new forecast track is near the various consensus
Lowell is still experiencing some easterly shear, which the models
suggest should abate some in the next 12 h or so. However, the
poor organization of the storm suggests it may take a while to
respond to the more favorable environment. Thus, the new intensity
forecast continues the trend of the old forecast in showing slow
strengthening for the first 36-48 h. After that time, the intensity
will be strongly dependent on where the center is in relation to the
strong sea-surface temperature gradient. Since the forecast track
is basically unchanged, the new intensity forecast has only minor
tweaks from the previous forecast based on the forecast track
keeping the system over 25-26C water temperatures through 120 h.
However, any motion north of the forecast track would bring the
center over colder water and lead to a system weaker than forecast,
while any motion south of the track would keep it over warmer water
and possibly allow the cyclone to become a hurricane. The intensity
forecast remains low confidence.