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Tropical Storm Lidia Forecast Discussion Number 11

2017-09-01 10:47:03| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Fri Sep 01 2017 000 WTPZ44 KNHC 010846 TCDEP4 Tropical Storm Lidia Discussion Number 11 NWS National Hurricane Center Miami FL EP142017 300 AM MDT Fri Sep 01 2017 Cloud top temperatures have been warming during the past few hours, and the convective pattern appears to be losing some organization as Lidia interacts with the high terrain of Baja California Sur. Still, Dvorak intensity estimates from TAFB and SAB remained T3.5, and the initial intensity is held at 55 kt. Recent ASCAT passes missed Lidia's core, but they did indicate a large swath of tropical-storm-force winds extending over the southern Gulf of California. Fixes suggest that Lidia has been moving more slowly during the past 6-12 hours, and the motion estimate is now toward the northwest (325 deg) at 7 kt. The storm is embedded between a mid-level high centered over the southwestern United States and a mid-level trough southwest over the Pacific, and these features should keep Lidia on a northwestward course for the next three days. Lidia's center is likely to move onshore south of Cabo San Lazaro later this morning and then cross on/off the western coast of the Baja California peninsula through 36 hours. While most of the track models are fairly well clustered, the GFS remains the fastest model, and the ECMWF is still one of the slowest. The new NHC forecast is a little faster than the previous one and lies between the GFS and ECMWF solutions, closest to TVCN and HCCA. Lidia is expected to weaken over the next couple of days, especially as the circulation continues to move over the Baja California peninsula. However, tropical-storm-force winds will continue to extend well east of the center, riding up the peninsula and adjacent Gulf of California for the next 36 hours. Once Lidia permanently moves off the west coast of the Baja California peninsula, it will be located over the cold waters of the California Current and will likely be unable to generate deep convection. For that reason, it should be a remnant low by 48 hours. After that time, Lidia will begin to interact with a deep-layer low located off the coast of California, and it is now expected to dissipate or be absorbed by that low by day 4. Since Lidia's center is expected to move onshore soon, and the storm is not likely to strengthen in the short time beforehand, the government of Mexico has discontinued the hurricane watch for southern Baja California Sur. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 23.8N 111.0W 55 KT 65 MPH 12H 01/1800Z 25.1N 111.9W 45 KT 50 MPH...INLAND 24H 02/0600Z 26.8N 113.4W 45 KT 50 MPH...NEAR COAST 36H 02/1800Z 28.1N 115.0W 35 KT 40 MPH...OVER WATER 48H 03/0600Z 29.3N 116.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 04/0600Z 31.8N 121.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 05/0600Z...DISSIPATED $$ Forecaster Berg

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Hurricane Irma Forecast Discussion Number 8

2017-09-01 10:45:03| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Sep 01 2017 000 WTNT41 KNHC 010844 TCDAT1 Hurricane Irma Discussion Number 8 NWS National Hurricane Center Miami FL AL112017 500 AM AST Fri Sep 01 2017 After rapidly strengthening on Thursday, Irma appears to have leveled off in intensity. The eye of the hurricane remains evident in satellite images, but it has occasionally been cloud filled. The deep convection in the eyewall has been fairly symmetric, and the Dvorak CI-numbers from TAFB and SAB have held steady at 5.5/102 kt. Based on these data, the initial wind speed remains 100 kt for this advisory. Although Irma is in a very low wind shear environment, the hurricane is moving over only marginally warm SSTs and is in close proximity to dry air. The models respond to these conditions by showing little change in strength or some weakening during the next couple of days. Thereafter, Irma is expected to move into a more favorable thermodynamic environment while remaining in low wind shear conditions, which should allow the hurricane to intensify. It should be noted that major hurricanes like Irma often undergo eyewall replacements that can cause fluctuations in strength, but unfortunately these internal dynamics can not be forecast with any accuracy. The NHC intensity forecast is identical to the previous one and lies near the high end of the model guidance. Irma is moving west-northwestward at 10 kt to the south of a subtropical high pressure system. This high is forecast to strengthen and build westward during the next few days, which should cause the hurricane to turn to the west in about 24 hours and then move to the west-southwest over the weekend. By the end of the forecast period, Irma is expected to move on the south side of the high, which should cause the storm to turn back to the west or west-northwest. Although the models agree on this overall scenario, they differ slightly on the strength and orientation of the high and the intensity of Irma. These differences have caused a fair amount of north-south spread. The NHC intensity forecast lies near the middle of the guidance envelope through day 4, but leans toward the southern end at day 5, in favor of the ECMWF and HCCA models. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 18.2N 36.5W 100 KT 115 MPH 12H 01/1800Z 18.5N 38.2W 100 KT 115 MPH 24H 02/0600Z 18.4N 40.5W 100 KT 115 MPH 36H 02/1800Z 18.2N 42.9W 100 KT 115 MPH 48H 03/0600Z 17.6N 45.2W 105 KT 120 MPH 72H 04/0600Z 16.5N 49.3W 110 KT 125 MPH 96H 05/0600Z 16.5N 53.5W 115 KT 130 MPH 120H 06/0600Z 17.5N 58.0W 120 KT 140 MPH $$ Forecaster Cangialosi

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Tropical Storm Lidia Forecast Discussion Number 10

2017-09-01 04:35:03| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Thu Aug 31 2017 000 WTPZ44 KNHC 010234 TCDEP4 Tropical Storm Lidia Discussion Number 10 NWS National Hurricane Center Miami FL EP142017 900 PM MDT Thu Aug 31 2017 During the past couple of hours while the center of Lidia was meandering very near the southern tip of the Baja California peninsula, the deep convection near the center blossomed, and the cloud pattern increased in organization. In fact, there was a hint of an eye feature in between two hooking bands. Part of the increase in convection could be related to the moist flow against the mountains. Based on recent satellite intensity estimates, the winds remain at 55 kt, and now that a large portion of the circulation is interacting with the peninsula, gradual weakening is anticipated. If the core of Lidia moves closer or over land as indicated in the NHC forecast, the weakening process could occur faster. Beyond 48 hours, the cold waters west of Baja California will finish the job. Lidia hesitated earlier this afternoon, but it has now resumed a motion toward the north-northwest or 335 degrees at about 9 kt. The steering pattern has not changed, and Lidia is still sandwiched between a high over Mexico and a cyclonic gyre to the west over the ocean. This flow will keep Lidia advancing over or very near the spine of the Baja California peninsula for the next day or two. Thereafter, the ridge will build to the north forcing the cyclone to move on a west-northwest to west track. By then, Lidia should be over cold waters as a shallow remnant low. Lidia continues to be a large system accompanied by very heavy rains which are occurring over portions of western Mexico and Baja California Sur. These rains are likely to produce life-threatening flash floods and mudslides. In addition, the mountainous terrain of the Baja California peninsula could enhance the winds at higher elevations. Some of the tropical moisture from Lidia may reach parts of the desert Southwest this holiday weekend, including southern California, southern Nevada and southwestern Arizona. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 23.3N 110.4W 55 KT 65 MPH 12H 01/1200Z 24.4N 111.2W 50 KT 60 MPH...INLAND 24H 02/0000Z 26.0N 112.3W 45 KT 50 MPH...NEAR THE COAST 36H 02/1200Z 27.3N 113.9W 40 KT 45 MPH...INLAND 48H 03/0000Z 28.7N 115.5W 30 KT 35 MPH...OVER WATER 72H 04/0000Z 30.5N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 05/0000Z 31.5N 122.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 06/0000Z 31.5N 125.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Avila

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Tropical Storm Lidia Forecast Discussion Number 9

2017-08-31 22:33:00| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Thu Aug 31 2017 000 WTPZ44 KNHC 312032 TCDEP4 Tropical Storm Lidia Discussion Number 9 NWS National Hurricane Center Miami FL EP142017 300 PM MDT Thu Aug 31 2017 Satellite imagery indicates that Lidia continues to become better organized, with convective bands now wrapping most of the way around a ragged clear-air center. Recent surface observations from the Cabo San Lucas area support increasing the initial intensity to 55 kt, although it is unclear how much terrain enhancement of these winds is occurring. The initial motion is north-northwestward or 335/7 kt between a mid-level anticyclone centered over central Mexico and a mid- to upper-level low located to the west over the Pacific. This motion should continue for the next 24 h or so. After that time, a mid-level anticyclone over the southwestern United States should become the main steering influence from 48-120 h, forcing Lidia to turn northwestward and eventually westward. The guidance has become somewhat less tightly spread, as the GFS is currently a right outlier showing a motion into the northern Gulf of California. Given the lack of support for this scenario from the other models, the new forecast track is similar to the previous track and a little south of the consensus models Additional strengthening is possible this evening before the center moves over the Baja California peninsula, and while the chance of Lidia becoming a hurricane is low it is still non-zero. Weakening is expected after 12 h due to the center moving up the spine of the Baja California peninsula, but tropical-storm-force winds are likely to spread up the Gulf of California well east of the center. Lidia is forecast to become a remnant low by 72 h due to interaction with land and cold water, and further weakening is anticipated over the cold waters west of the northern Baja California peninsula at 96 and 102 h. Lidia is a large system accompanied by very heavy rains which are already occurring over portions of western Mexico and Baja California Sur. Regardless of how strong Lidia becomes, life-threatening flash floods and mudslides will be a significant hazard over these areas. In addition, the mountainous terrain of the Baja California peninsula could enhance the winds at higher elevations. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 22.7N 110.1W 55 KT 65 MPH 12H 01/0600Z 23.8N 110.7W 60 KT 70 MPH 24H 01/1800Z 25.2N 111.7W 50 KT 60 MPH...INLAND 36H 02/0600Z 26.8N 113.0W 45 KT 50 MPH...INLAND 48H 02/1800Z 28.2N 114.4W 40 KT 45 MPH...OVER WATER 72H 03/1800Z 30.0N 117.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 04/1800Z 30.5N 120.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 05/1800Z 30.5N 123.0W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Hurricane Irma Forecast Discussion Number 6

2017-08-31 22:32:35| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Aug 31 2017 000 WTNT41 KNHC 312032 TCDAT1 Hurricane Irma Discussion Number 6 NWS National Hurricane Center Miami FL AL112017 500 PM AST Thu Aug 31 2017 Irma has become an impressive hurricane with intense eyewall convection surrounding a small eye. Satellite estimates continue to rapidly rise, and the Dvorak classifications from both TAFB & SAB support an initial wind speed of 100 kt. This is a remarkable 50-kt increase from yesterday at this time. Microwave and satellite data suggest that an eyewall replacement cycle could be starting. This isn't surprising given how small the eye is, and will probably be the first of many eyewall cycles for this hurricane. Overall, Irma should be in a low-shear environment for several days, with the intensity controlled by eyewall cycles and the moderately warm SSTs along the path. Thus the forecast intensity is leveled off for the next 2 days. After the weekend, Irma should be moving over much warmer water, with SSTs forecast to be 29C at the end of the period. All indications are for Irma to be strengthening by the end of the forecast period, with the NHC prediction adjusted slightly upward from the previous one, in line with the extremely low pressures forecast by the global and regional hurricane models at that time. Irma continues moving west-northwestward, now at about 10 kt. There has been no change to the forecast philosophy, with the hurricane likely to turn westward and west-southwestward over the next few days due to a building ridge over the central Atlantic. At long range, however, model guidance is not in good agreement on the strength of the ridge, resulting in some significant north-south differences in the global models. I am inclined to stay on the southwestern side of the model guidance, given the rather consistent forecasts of the ECMWF and its ensemble. In addition, the strongest members of the recent ensembles are on the southern side on the consensus, giving some confidence in that approach. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 17.3N 34.8W 100 KT 115 MPH 12H 01/0600Z 17.8N 36.2W 105 KT 120 MPH 24H 01/1800Z 18.2N 38.3W 105 KT 120 MPH 36H 02/0600Z 18.3N 40.7W 105 KT 120 MPH 48H 02/1800Z 17.9N 42.9W 105 KT 120 MPH 72H 03/1800Z 16.8N 47.5W 110 KT 125 MPH 96H 04/1800Z 16.0N 52.0W 115 KT 130 MPH 120H 05/1800Z 16.5N 56.5W 120 KT 140 MPH $$ Forecaster Blake

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