Hurricane Calvin Discussion Number 17 NWS National Hurricane Center Miami FL EP032023 1100 AM HST Sat Jul 15 2023
The satellite appearance of Calvin has shown some ill effects today from cooler SSTs and some drier air in its surrounding environment. A 1512 UTC SSMIS 89 GHz passive microwave image of the hurricane showed the eyewall was open to the east, where a dry slot was noted earlier wrapping around that portion of the circulation. Since then, the eye has become a bit warmer and more pronounced in infrared satellite imagery, and some deeper inner-core convection has wrapped around the center. The latest objective and subjective satellite intensity estimates range from 77-90 kt. Based on a blend of these data and recent satellite trends, the initial intensity is held at 85 kt for this advisory.
Weakening is expected during the next few days as the cyclone moves into a drier and more stable air mass over sub-26C SSTs. In fact, model-simulated satellite imagery from the GFS and ECMWF suggest Calvin could lose most, or briefly all, of its convection once it enters the central Pacific basin. However, the underlying SSTs become slightly warmer between 48-96 h while the deep-layer shear diagnosed by the global models is low to moderate. Therefore, it seems that Calvin could regenerate new bursts of convection on its approach to Hawaii, which is shown by the global and hurricane models. Therefore, the NHC forecast keeps Calvin a tropical cyclone through 96 h. Regardless of its status, the cyclone appears likely to maintain some tropical-storm-force winds in the northern portion of its circulation as it approaches Hawaii. The global model fields suggest the system will be close to opening into a trough by or shortly after day 5.
The long-term motion of Calvin is westward at 280/14 kt. A westward to west-northwestward motion will continue through the forecast period as the cyclone is steered by a mid-level ridge entrenched over the eastern Pacific. Calvin is forecast to cross 140W and enter the central Pacific basin on Monday morning and approach the Hawaiian Islands on Tuesday into early Wednesday. The various track models continue to bring Calvin near or over the Big Island of Hawaii, but exactly where it will track relative to the island is still unclear given the cross-track spread noted at day 3 and beyond. The updated NHC forecast has been adjusted slightly faster than the previous one, but otherwise very little change was made.
KEY MESSAGES:
1. Calvin is forecast to move across the central Pacific Ocean and approach the Hawaiian Islands early next week. It is too early to determine the exact location and magnitude of potential impacts given uncertainties in the track, intensity, and structure of Calvin as it approaches the islands. Interests in Hawaii should closely monitor the latest forecast updates.
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Hurricane Calvin Discussion Number 18 NWS National Hurricane Center Miami FL EP032023 500 PM HST Sat Jul 15 2023
During the past several hours, the satellite cloud pattern of Calvin has been unsteady, with the eye coming and going and the eyewall cloud top temperatures fluctuating. Overall, though, there has been little change in the organization and the various satellite intensity estimates. Based on this, the initial intensity is again held at 85 kt, which is close to the CIMMS satellite consensus estimate.
Calvin is currently over 25C sea surface temperatures, and it should be over 24C water in about 24 h. This should cause weakening during the next 24-36 h. After that time, the sea surface temperatures start to increase under the forecast track, although they are expected to stay below 26C until the system passes near Hawaii. During this period, the vertical wind shear is forecast to be light to moderate. The consensus of the guidance during this time is that Calvin will continue to weaken while producing intermittent bursts of convection, and that is the basis for keeping it a tropical storm. Regardless of how much convection is present, it appears likely that Calvin will maintain tropical-storm-force winds as it passes near the Big Island of Hawaii. After 96 h, stronger shear should cause the cyclone to degenerate to a remnant low pressure area or trough.
The initial motion is now 285/15 kt. As in the previous forecast, a westward to west-northwestward motion will continue through the forecast period as the cyclone is steered by a mid-level ridge entrenched over the eastern Pacific. On the forecast track, Calvin is forecast to cross 140W and enter the central Pacific basin on Monday morning and approach the Hawaiian Islands on Tuesday into early Wednesday. There remains some cross-track spread in the models, so while the new forecast track calls for Calvin to pass close to the Big Island of Hawaii it remains unclear exactly how it will track relative to the island. The new forecast track has only minor adjustments from the previous track.
KEY MESSAGES:
1. Calvin is forecast to move across the central Pacific Ocean and approach the Hawaiian Islands early next week. It is too early to determine the exact location and magnitude of potential impacts given uncertainties in the track, intensity, and structure of Calvin as it approaches the islands. Interests in Hawaii should closely monitor the latest forecast updates.
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Hurricane Calvin Discussion Number 19 NWS National Hurricane Center Miami FL EP032023 1100 PM HST Sat Jul 15 2023
The cloud pattern and overall organization of Calvin has been deteriorating this evening. The eye and eyewall are unraveling and opening up on the western side. Dry air entrainment and cool water temperatures are also causing the convective banding to diminish with cloud tops warming and the inner core dissipating. Subjective Dvorak estimates, as well as CIMMS ADT and AiDT estimates, have come down with this advisory ranging from 55 kt to 78 kt. Based on these data, the initial intensity is lowered to 70 kt.
Calvin is currently moving over cooler SSTs near 25C and will continue to be over even cooler water temps the next 24-36 hours. Calvin is also moving into a drier mid-level airmass and a more stable environment. Given the current satellite trends and the environment Calvin is beginning to encounter, weakening is forecast for the remainder of the period. However, the system is still likely to continue to have bursts of convection as it approaches the Hawaiian Islands in a few days. Regardless of how much convection is present, it appears likely that Calvin will maintain tropical storm force winds as it passes near the Big Island of Hawaii. After it passes Hawaii, stronger shear should cause the cyclone to degenerate to a remnant low pressure area or trough.
The initial motion is estimated to be 285/15 kt. A westward to west-northwestward motion will continue through the forecast period as the cyclone remains steered by a mid-level ridge over the eastern Pacific. On the forecast track, Calvin is forecast to cross 140W and enter the central Pacific basin Sunday night or early Monday morning and approach the Hawaiian Islands on Tuesday into early Wednesday. There remains some cross-track spread in the models, so while the new forecast track calls for Calvin to pass close to the Big Island of Hawaii it remains unclear exactly how it will track relative to the island. The new forecast track has only minor adjustments from the previous track.
KEY MESSAGES:
1. Calvin is forecast to move across the central Pacific Ocean and approach the Hawaiian Islands within the next few days. Interests in Hawaii should closely monitor the latest forecast updates and a Tropical Storm Watch could be issued for portions of the main Hawaiian Islands late Sunday.
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Tropical Storm Calvin Discussion Number 20...Corrected NWS National Hurricane Center Miami FL EP032023 500 AM HST Sun Jul 16 2023
Corrected timing in the key messages
The cloud pattern of Calvin has further deteriorated this morning. The center is now exposed, and cloud tops have warmed over much of the circulation with only a small area of moderate to deep convection noted to the east of the center. The objective and subjective satellite intensity estimates continue to quickly decline, with a blend of the recent data suggesting that Calvin is no longer a hurricane. Based on these data and its poor satellite structure, the initial intensity is lowered to 60 kt.
The track forecast remains straightforward. Calvin is expected to keep moving generally westward for the next several days as it is steered by a well-established ridge over the eastern Pacific. This motion will bring the cyclone into the central Pacific basin (west of 140W) tonight or early Monday morning. Calvin is forecast to approach the Hawaiian Islands on Tuesday and pass near or over the Big Island of Hawaii early Wednesday. The track guidance remains in good agreement on this overall scenario, although the details of its track near Hawaii are still uncertain given the average amount of cross-track spread in the guidance. The latest NHC forecast is slightly faster and has been nudged slightly northward at 60-96 h, but still lies near the center of the guidance envelope and close to the HCCA and TVCE aids.
Calvin will move over 24 deg C waters and into a drier, more stable environment during the next couple of days. Therefore, continued weakening is anticipated, and the system could struggle to produce convection on its trek into the central Pacific basin. As Calvin moves closer to Hawaii, model-simulated satellite imagery suggests it could produce some renewed bursts of convection to the north of its center. This forecast keeps Calvin as a tropical cyclone through 72 h, although it could become post-tropical sooner if convection collapses for an extended period. Regardless, there is good support from both the global and hurricane models that Calvin will maintain some tropical-storm-force winds (mainly to the north of its center) as it nears Hawaii. With strong deep-layer southwesterly shear expected in 96-120 h, this forecast shows Calvin opening into a trough and dissipating by day 5.
KEY MESSAGES:
1. Calvin is forecast to move across the central Pacific Ocean and approach the Hawaiian Islands during the next few days. A Tropical Storm Watch could be issued for portions of the main Hawaiian Islands later today, and interests in Hawaii should closely monitor the latest forecast updates.
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