Hurricane Genevieve Discussion Number 7
NWS National Hurricane Center Miami FL EP122020
900 PM MDT Mon Aug 17 2020
Genevieve's rapid intensification phase continues, having
strengthened 40 kt over the past 24 hours. The upper-level outflow
pattern has continued to expand, and outflow channels to the north
and south have become evident in water vapor imagery and UW-CIMSS
upper-level wind analyses. A 20-nmi-wide, cloud-filled eye has
appeared in infrared and visible satellite imagery during the past
few hours, indicating that Genevieve's wind field and vertical
structure has improved significantly since the previous advisory.
Subjective satellite intensity estimates are T5.0/90 kt from TAFB
and T4.5/77 kt from SAB, while objective estimates are T4.7/82 kt
from UW-CIMSS ADT and T5.1/92 kt from the NHC. An average of these
estimates supports an initial intensity of 85 kt.
Genevieve has remained a well-behaved hurricane and lies on the
previous advisory track, maintaining a motion of 300/15 kt. The
hurricane is expected to continue moving west-northwestward for the
next 12 hours or so while the cyclone skirts the southwestern
periphery of a broad deep-layer ridge. A slight motion shift toward
the northwest is forecast during the 24-48 hour period, bringing
Genevieve's outer wind field a little closer to Baja California Sur.
Thereafter, a motion back toward the west-northwest is forecast,
which will keep the center of the hurricane moving parallel to but
offshore the west coast of Baja California Sur. The new NHC forecast
track is essentially just an extension of the previous advisory
track, and lies down the middle of the tightly packed simple and
corrected-consensus models.
Genevieve is forecast to continue its rapid intensification phase
for the next 36 hours or so while the hurricane moves within an
extremely favorable environment characterized by low vertical wind
shear less than 5 kt, dual outflow channels, sea-surface
temperatures (SSTs) of 29-30C, and a very moist middle-troposphere.
By 48 hours, the hurricane will be moving over upper-ocean heat
content values of less than 5 units due to shallow warm ocean layer,
likely resulting in significant cold upwelling occurring. This
should initiate a gradual weakening trend, followed by rapid
weakening after 60 hours when Genevieve will be moving over sub-25
deg C water. By 120 hours, the hurricane is expected to degenerate
into a convection-free post-tropical cyclone over 21 deg C SSTs. The
NHC official intensity forecast remains near the the upper end of
the intensity guidance, and is similar to the previous advisory.
Key Messages:
1. There is an increasing risk of tropical-storm-force winds over
the southern portion of the Baja California peninsula beginning
Wednesday afternoon and continuing into Thursday as Genevieve passes
near or southwest of the southern tip of Baja California, and a
Tropical Storm Watch is in effect for a portion of this area.
2. Large swells generated by Genevieve are affecting portions of the
coast of southern Mexico and will spread northward along the coast
of Mexico to the Baja California peninsula by Wednesday.
FORECAST POSITIONS AND MAX WINDS
INIT 18/0300Z 16.5N 106.0W 85 KT 100 MPH
12H 18/1200Z 17.5N 107.5W 100 KT 115 MPH
24H 19/0000Z 18.9N 109.3W 115 KT 130 MPH
36H 19/1200Z 20.1N 110.5W 120 KT 140 MPH
48H 20/0000Z 21.2N 111.4W 115 KT 130 MPH
60H 20/1200Z 22.3N 112.5W 100 KT 115 MPH
72H 21/0000Z 23.3N 113.8W 85 KT 100 MPH
96H 22/0000Z 25.4N 117.0W 60 KT 70 MPH
120H 23/0000Z 27.9N 120.5W 40 KT 45 MPH...POST-TROPICAL
$$
Forecaster Stewart
