Hurricane Grace Discussion Number 24
NWS National Hurricane Center Miami FL AL072021
400 AM CDT Thu Aug 19 2021
After a brief convective hiatus between 0400-0700 UTC, deep
convection in the inner-core region has increased and become better
organized during the past couple of hours. An Air Force Reserve
Hurricane Hunter aircraft investigating Grace more than 4 hours ago
reported a central pressure of 986 mb -- down 2 mb from previous
passes -- and a maximum 700-mb flight-level wind speed of 74 kt on
its last leg northbound around 0500 UTC. The 74-kt flight-level wind
equates to about a 67-kt surface wind speed. These data supported
maintaining a 70-kt intensity at 0600 UTC. The upper-level outflow
remains symmetrical and has been expanding somewhat over the past
few hours.
The initial motion is 280/15 kt based on the earlier recon fixes and
passive microwave satellite data. Grace should continue to move
generally westward for the next 48 hours, crossing the coast of the
eastern Yucatan Peninsula within the next couple of hours, followed
by a track across the Yucatan and emergence over the Bay of Campeche
by 24 hours, with a subsequent landfall along the eastern coast of
mainland Mexico shortly after the 48-hour forecast period. This
track scenario is consistent with the latest 0000 UTC global and
regional models, which show the strong deep-layer ridge to the north
of Grace maintaining its expansive presence across the western
Atlantic, Gulf of Mexico, and northern Mexico. After the second
landfall, Grace is expected to turn west-southwestward and
dissipate over the mountains of central Mexico by 72 hours. The new
NHC forecast track is similar to the previous advisory track, and
lies along the northern edge of the tightly packed consensus track
models.
Given the recent improvement in Grace's inner-core convective
structure noted in high-resolution infrared satellite imagery, some
slight strengthening to 75 kt could still occur just prior to
landfall this morning. Weakening will commence once Grace moves
inland over Yucatan, with re-strengthening expected after the
cyclone emerges over the Bay of Campeche where the vertical wind
shear is forecast to decrease below 10 kt. Grace is expected to be a
hurricane when the second landfall occurs along the coast of
mainland Mexico, with the cyclone possibly reaching a peak
intensity of 75 kt shortly after the 48-hour period. After final
landfall in mainland Mexico, Grace should quickly weaken and
dissipate over the mountains of Mexico by 72 hours, if not sooner.
The remnants of Grace are expected to emerge over the eastern North
Pacific and possibly re-develop there, but the uncertainty of
whether this will be the original center or a new center precludes
forecast points over the Pacific at this time.
A Hurricane Warning will likely be required for portions of the
Hurricane Watch area of mainland Mexico later this morning or
afternoon.
Key Messages:
1. Hurricane conditions and a dangerous storm surge are expected
in portions of the Hurricane Warning area in the eastern Yucatan
Peninsula of Mexico during the next several hours. Preparations to
protect life and property should be rushed to completion.
2. There is an increasing risk of hurricane conditions and dangerous
storm surge in portions of eastern mainland Mexico beginning late
Friday, and a Hurricane Watch is in effect for part of this area.
3. Through the weekend, heavy rainfall across central and northern
portions of the Yucatan Peninsula and Veracruz State should lead to
flash and urban flooding. In addition, the heavy rainfall from Grace
will be capable of producing mudslides in Veracruz.
FORECAST POSITIONS AND MAX WINDS
INIT 19/0900Z 20.0N 87.2W 70 KT 80 MPH
12H 19/1800Z 20.3N 89.7W 50 KT 60 MPH...INLAND
24H 20/0600Z 20.6N 92.6W 60 KT 70 MPH...OVER WATER
36H 20/1800Z 20.5N 95.0W 70 KT 80 MPH
48H 21/0600Z 20.1N 97.3W 55 KT 65 MPH...INLAND
60H 21/1800Z 19.7N 100.1W 20 KT 25 MPH...POST-TROP/INLAND
72H 22/0600Z...DISSIPATED
$$
Forecaster Stewart
NWS National Hurricane Center Miami FL AL072021
400 AM CDT Thu Aug 19 2021
After a brief convective hiatus between 0400-0700 UTC, deep
convection in the inner-core region has increased and become better
organized during the past couple of hours. An Air Force Reserve
Hurricane Hunter aircraft investigating Grace more than 4 hours ago
reported a central pressure of 986 mb -- down 2 mb from previous
passes -- and a maximum 700-mb flight-level wind speed of 74 kt on
its last leg northbound around 0500 UTC. The 74-kt flight-level wind
equates to about a 67-kt surface wind speed. These data supported
maintaining a 70-kt intensity at 0600 UTC. The upper-level outflow
remains symmetrical and has been expanding somewhat over the past
few hours.
The initial motion is 280/15 kt based on the earlier recon fixes and
passive microwave satellite data. Grace should continue to move
generally westward for the next 48 hours, crossing the coast of the
eastern Yucatan Peninsula within the next couple of hours, followed
by a track across the Yucatan and emergence over the Bay of Campeche
by 24 hours, with a subsequent landfall along the eastern coast of
mainland Mexico shortly after the 48-hour forecast period. This
track scenario is consistent with the latest 0000 UTC global and
regional models, which show the strong deep-layer ridge to the north
of Grace maintaining its expansive presence across the western
Atlantic, Gulf of Mexico, and northern Mexico. After the second
landfall, Grace is expected to turn west-southwestward and
dissipate over the mountains of central Mexico by 72 hours. The new
NHC forecast track is similar to the previous advisory track, and
lies along the northern edge of the tightly packed consensus track
models.
Given the recent improvement in Grace's inner-core convective
structure noted in high-resolution infrared satellite imagery, some
slight strengthening to 75 kt could still occur just prior to
landfall this morning. Weakening will commence once Grace moves
inland over Yucatan, with re-strengthening expected after the
cyclone emerges over the Bay of Campeche where the vertical wind
shear is forecast to decrease below 10 kt. Grace is expected to be a
hurricane when the second landfall occurs along the coast of
mainland Mexico, with the cyclone possibly reaching a peak
intensity of 75 kt shortly after the 48-hour period. After final
landfall in mainland Mexico, Grace should quickly weaken and
dissipate over the mountains of Mexico by 72 hours, if not sooner.
The remnants of Grace are expected to emerge over the eastern North
Pacific and possibly re-develop there, but the uncertainty of
whether this will be the original center or a new center precludes
forecast points over the Pacific at this time.
A Hurricane Warning will likely be required for portions of the
Hurricane Watch area of mainland Mexico later this morning or
afternoon.
Key Messages:
1. Hurricane conditions and a dangerous storm surge are expected
in portions of the Hurricane Warning area in the eastern Yucatan
Peninsula of Mexico during the next several hours. Preparations to
protect life and property should be rushed to completion.
2. There is an increasing risk of hurricane conditions and dangerous
storm surge in portions of eastern mainland Mexico beginning late
Friday, and a Hurricane Watch is in effect for part of this area.
3. Through the weekend, heavy rainfall across central and northern
portions of the Yucatan Peninsula and Veracruz State should lead to
flash and urban flooding. In addition, the heavy rainfall from Grace
will be capable of producing mudslides in Veracruz.
FORECAST POSITIONS AND MAX WINDS
INIT 19/0900Z 20.0N 87.2W 70 KT 80 MPH
12H 19/1800Z 20.3N 89.7W 50 KT 60 MPH...INLAND
24H 20/0600Z 20.6N 92.6W 60 KT 70 MPH...OVER WATER
36H 20/1800Z 20.5N 95.0W 70 KT 80 MPH
48H 21/0600Z 20.1N 97.3W 55 KT 65 MPH...INLAND
60H 21/1800Z 19.7N 100.1W 20 KT 25 MPH...POST-TROP/INLAND
72H 22/0600Z...DISSIPATED
$$
Forecaster Stewart