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Tropical Storm Henri Forecast Discussion Number 13
2021-08-19 05:00:12| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Aug 18 2021 000 WTNT43 KNHC 190300 TCDAT3 Tropical Storm Henri Discussion Number 13 NWS National Hurricane Center Miami FL AL082021 1100 PM AST Wed Aug 18 2021 Henris appearance this evening is one of a tropical cyclone that is battling vertical wind shear. The satellite structure has evolved into a large convective plume with overshooting cold -70 to -75 C cloud top temperatures near the center of the convective mass. Underneath the cirrus, Henris structure has remained steady-state, with a SSMIS pass at 2243Z showing a ragged mid-level eye on the 91 GHz channel that remains displaced a bit southeast of the low-level signature on 37 GHz. The latest satellite intensity estimates have a large spread in values ranging from 55-kt up to 80-kt. I have elected to maintain Henris intensity at 60 kt for this advisory, but there is a larger than normal uncertainty in this estimate. The initial motion continues to be just south of due west at 265/8 kt. The short-term track guidance is in general agreement that Henri will continue a general westward motion for the next day or so, as the cyclone is caught to the south of a pronounced mid- to upper-level ridge. However, the models disagree on how far westward Henri is able to advance in the short-term, and these track differences appear to be related to Henri's intensity and vertical depth of the circulation. This track dependency is nicely illustrated by the most recent ECMWF ensemble guidance, where stronger members move further south and west in the short-term, ending up on the left-side of the ensemble mean, while weaker members move slower and more poleward. The deterministic guidance is similar, with the weaker ECMWF and Canadian runs off to the east/right while the stronger GFS and UKMET runs are further left/west. These short-term track differences appear pivotal, because the ridge over Henri is then expected to quickly erode as a mid-latitude trough digs in over the Ohio Valley and becomes negatively tilted over the Mid-Atlantic. The leftward track guidance has Henri interacting with this trough leading to a track forecast much closer to the northeastern US, while the rightward track guidance is not captured by this feature, and stay further offshore escaping out to sea. In general, the mean of the track guidance is very similar, or just a shade to the right of the previous cycle. I have elected to maintain a very similar track to the previous advisory, splitting the difference between the previous forecast just left, and the reliable HCCA consensus aid just right. As mentioned previously, a NOAA Gulfstream IV aircraft has been scheduled to investigate the synoptic environment of Henri tomorrow and will hopefully provide more data ingested into the model guidance to reduce the large track spread seen in the current cycle. Henri is now under moderate northerly shear that is forecast to increase to 25-30 knots over the next 24 hours. While this would ordinarily weaken the tropical cyclone, the system also remains under very warm 29-30 C sea-surface temperatures that are somewhat above normal for this time of year. Due to these offsetting factors, the latest NHC intensity forecast maintains Henri at 60-kt for the next 24 hours. Afterwards, the shear is forecast to decrease as the storm turns more poleward directly under the upper-level ridge axis. This favorable synoptic pattern should allow Henri to intensify and gradual intensification is shown up to a 80-kt peak in 72-h. The NHC intensity forecast is more or less in the mean of the large guidance spread, though it should be noted that the regional hurricane models (HWRF, HMON, COAMPS-TC) have somewhat stronger peak intensities later in the forecast period. Key Messages: 1. The forecast track of Henri remains near the northeast coast of the U.S. this weekend and early next week, and the risks of storm surge, wind, and rain impacts in portions of the northeastern U.S. and Atlantic Canada remains a distinct possibility. Interests in these areas should closely follow the progress of Henri and check for updates to the forecast. 2. Swells from Henri will begin to reach much of the east coast of the U.S. and Atlantic Canada by the end of the week and continue through the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 29.8N 68.5W 60 KT 70 MPH 12H 19/1200Z 29.8N 69.9W 60 KT 70 MPH 24H 20/0000Z 30.0N 71.8W 60 KT 70 MPH 36H 20/1200Z 30.7N 72.7W 65 KT 75 MPH 48H 21/0000Z 32.3N 72.8W 70 KT 80 MPH 60H 21/1200Z 34.4N 71.8W 75 KT 85 MPH 72H 22/0000Z 36.9N 70.7W 80 KT 90 MPH 96H 23/0000Z 40.4N 69.4W 70 KT 80 MPH 120H 24/0000Z 41.8N 68.3W 60 KT 70 MPH $$ Forecaster Papin/Beven
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Hurricane Grace Forecast Discussion Number 23
2021-08-19 04:55:38| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Wed Aug 18 2021 000 WTNT42 KNHC 190255 TCDAT2 Hurricane Grace Discussion Number 23 NWS National Hurricane Center Miami FL AL072021 1000 PM CDT Wed Aug 18 2021 Grace has become a bit better organized during the past several hours. Cuban radar data indicates that the eye and eyewall have become better defined, and reports from Air Force Reserve and NOAA Hurricane Hunter aircraft show that the inner core circulation has become better defined. There are also occasional attempts at eye formation in satellite imagery. However, these changes have not yet resulted in significant intensification, with the maximum winds remaining near 70 kt and the central pressure hovering near 988 mb. One possible restraint on development is a dry slot that is seen wrapping around the central core in both satellite imagery and Cuban radar data. The center has jogged a little to the left during the past few hours, and the initial motion is now 280/16. The hurricane should continue to move generally westward to west-northwestward for the next 24-36 h, followed by a westward to west-southwestward motion from 36-48 h. This motion should bring the center over the Yucatan Peninsula of Mexico during the next 12 h, followed by passage across the southwestern Gulf of Mexico or the Bay of Campeche to a second landfall in mainland Mexico between 48-60 h. After that, the cyclone should continue moving into the mountains of Mexico until it dissipates. The new forecast track is nudged a little south of the previous forecast, and it lies near the various consensus models. Except for the aforementioned dry slot, conditions appear favorable for intensification before landfall on the Yucatan peninsula. While not explicitly show in the intensity forecast, Grace could reach an intensity of 75-80 kt before it reaches Yucatan. The cyclone should weaken some as it crosses the peninsula, then re-intensify over the Gulf of Mexico until it reaches mainland Mexico. After final landfall in Mexico, Grace is expected to quickly weaken and dissipate over the mountains of Mexico just after 72 h. The remnants of Grace are likely to emerge in the 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 Watch and a Tropical Storm Watch have been issued for portions of mainland Mexico. 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 beginning 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 has been issued 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 19/0300Z 19.8N 85.6W 70 KT 80 MPH 12H 19/1200Z 20.3N 88.1W 70 KT 80 MPH...INLAND 24H 20/0000Z 20.6N 91.4W 60 KT 70 MPH...OVER WATER 36H 20/1200Z 20.7N 94.0W 65 KT 75 MPH 48H 21/0000Z 20.5N 96.1W 75 KT 85 MPH 60H 21/1200Z 20.0N 98.8W 35 KT 40 MPH...INLAND 72H 22/0000Z 19.7N 101.6W 20 KT 25 MPH...POST-TROP/INLAND 96H 23/0000Z...DISSIPATED $$ Forecaster Beven
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Hurricane Linda Forecast Discussion Number 36
2021-08-19 04:52:41| Tropical Depression LIDIA
Issued at 500 PM HST Wed Aug 18 2021
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Tropical Storm Henri Forecast Discussion Number 12
2021-08-18 22:49:34| National Hurricane Center (Atlantic)
Issued at 500 PM AST Wed Aug 18 2021 356 WTNT43 KNHC 182049 TCDAT3 Tropical Storm Henri Discussion Number 12 NWS National Hurricane Center Miami FL AL082021 500 PM AST Wed Aug 18 2021 Henri appears a little better organized this afternoon. The storm still has a central dense overcast pattern and there have been hints of an eye evident in visible satellite images. Microwave images continue to show a mid-level eye feature, but the storm does not appear quite as well organized in the low-levels, and the vortex is still titled southward with height. The latest Dvorak estimates range from 55 to 67 kt, and based on that data the initial intensity is nudged up to 60 kt, just below hurricane strength. Henri is moving just south of due west at a slightly faster pace now, 265/8 kt. The storm is expected to continue westward for another 36 hours or so as it moves in the flow on the south side of a mid-level ridge. A gradual turn to the north is forecast to begin on Friday when a cutoff low forms over the Ohio Valley and the northeastern U.S. This general northward motion should continue through the weekend as another ridge builds to the east of Henri over the northwestern Atlantic. The models continue their westward shift, and the NHC track forecast has again been adjusted in that direction and no longer shows a northeastward motion out to sea. In particular, the westward adjustment at day 5 was a sizable 150 miles, and even with this shift the NHC forecast is still a little to the east of some of the consensus aids. NOAA Gulfstream IV missions and special weather balloon soundings have been scheduled, and it is hoped that this additional data will help the models handle the evolving steering pattern. Given the uncertainty in the longer range track forecast, users should be prepared for additional adjustments to the NHC track prediction in future forecast cycles. The storm is currently in an environment of about 15-20 kt of northerly wind shear according to the SHIPS model and analyses from CIMSS at the University of Wisconsin, which is the reason the vortex is currently titled. The shear should persist for another day or so, and little change in strength seems likely during that time period. However, strengthening is expected on Friday and Saturday as the shear decreases while the storm remains over the Gulf Stream. Some weakening seems likely at days 4 and 5 when the storm is expected to be over cooler waters. The NHC intensity forecast lies roughly near the middle of the guidance envelope and only minor changes were made to the previous prediction. Key Messages: 1. The forecast track of Henri has shifted toward the northeast coast of the U.S. this weekend and early next week, increasing the risk of direct storm surge, wind, and rain impacts in portions of the northeastern U.S. and Atlantic Canada during that time. Interests in these areas should closely follow the progress of Henri and check for updates to the forecast. 2. Swells from Henri will begin to reach much of the east coast of the U.S. and Atlantic Canada by the end of the week and continue through the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 29.9N 67.6W 60 KT 70 MPH 12H 19/0600Z 29.8N 69.0W 60 KT 70 MPH 24H 19/1800Z 29.8N 70.7W 60 KT 70 MPH 36H 20/0600Z 30.1N 72.3W 65 KT 75 MPH 48H 20/1800Z 31.0N 73.2W 70 KT 80 MPH 60H 21/0600Z 32.7N 72.7W 75 KT 85 MPH 72H 21/1800Z 35.2N 71.7W 80 KT 90 MPH 96H 22/1800Z 39.3N 70.0W 70 KT 80 MPH 120H 23/1800Z 41.4N 69.8W 60 KT 70 MPH $$ Forecaster Cangialosi
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Hurricane Grace Forecast Discussion Number 22
2021-08-18 22:44:33| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Wed Aug 18 2021 000 WTNT42 KNHC 182044 TCDAT2 Hurricane Grace Discussion Number 22 NWS National Hurricane Center Miami FL AL072021 500 PM EDT Wed Aug 18 2021 A ragged eye appeared for a while on visible satellite imagery, but it has recently been obscured by cumulonimbus tops. The overall cloud pattern has been maintaining its organization with some convective banding features and very cold cloud tops, mainly over the eastern portion of the circulation. The current intensity estimate is set at 70 kt, which is a blend of Dvorak estimates from TAFB and SAB. Another Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate the hurricane in a few hours to provide another intensity estimate. Grace will continue to move over waters of very high oceanic heat content prior to reaching the east coast of the Yucatan Peninsula, which of course favors intensification. Aside from moderate northwesterly shear, a possible impediment to strengthening is a northeast to southwest-oriented shear axis located just to the northwest of the hurricane. Nonetheless, some intensification is anticipated before landfall in Yucatan, with restrengthening over the Bay of Campeche. The official intensity forecast continues to be in general agreement with the multi-model consensus predictions, IVCN and HCCA. Grace is moving west-northwestward, or about 285/14 kt. There has been essentially no change to the track forecast philosophy. Grace should maintain a west-northwestward to westward motion, on the southern periphery of a strong subtropical ridge, for the next several days. The official track forecast is very similar to the previous one and about on top of the latest multi-model consensus, TVCA. A Hurricane Watch will likely be required for a portion of the coast of eastern mainland Mexico tonight. 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 beginning late tonight or early Thursday. 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 will likely be issued for part of this area tonight. 3. Through the weekend, heavy rainfall across the Cayman Islands as well as 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 18/2100Z 19.7N 83.7W 70 KT 80 MPH 12H 19/0600Z 20.2N 86.1W 75 KT 85 MPH 24H 19/1800Z 20.7N 89.3W 55 KT 65 MPH...INLAND 36H 20/0600Z 20.9N 92.2W 60 KT 70 MPH...OVER WATER 48H 20/1800Z 20.8N 94.6W 70 KT 80 MPH...OVER WATER 60H 21/0600Z 20.4N 97.3W 75 KT 85 MPH...INLAND 72H 21/1800Z 20.0N 99.9W 30 KT 35 MPH...INLAND 96H 22/1800Z 19.5N 104.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 23/1800Z...DISSIPATED $$ Forecaster Pasch
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