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Hurricane Gert Forecast Discussion Number 17

2017-08-17 04:32:16| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Aug 16 2017 000 WTNT43 KNHC 170232 TCDAT3 Hurricane Gert Discussion Number 17 NWS National Hurricane Center Miami FL AL082017 1100 PM AST Wed Aug 16 2017 Gert has maintained an eye with very cold cloud tops mainly over the northern and western portions of the circulation, which is rather remarkable for a system at 40N latitude. The current intensity is set a little higher, to 90 kt, in agreement with the latest Dvorak estimates from TAFB and SAB. The cyclone has continued to traverse warm waters, but very soon will encounter a much cooler ocean to the north of the Gulf Stream. Thus, rapid weakening is forecast, similar to the latest model consensus. In 36 hours the global model guidance depicts the system becoming embedded in a distinct baroclinic zone, so Gert should have become an extratropical storm by that time. The extratropical cyclone is forecast to merge with another large low over the north Atlantic after 72 hours. Gert has continued to accelerate and is now moving east-northeastward near 32 kt. A slightly faster motion is expected on Thursday in the strong flow to the southeast of a mid-tropospheric cyclone nearing Newfoundland. Later in the forecast period, the post-tropical system is likely to turn northeastward and slow down significantly while it interacts with the other large low. The track, intensity, and wind radii forecasts have incorporated guidance from NOAA's Ocean Prediction Center. Swells from Gert should continue to affect the northeast U.S. coast and Atlantic Canada through Thursday. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local weather forecast office for more information. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 40.1N 58.4W 90 KT 105 MPH 12H 17/1200Z 42.6N 52.1W 75 KT 85 MPH 24H 18/0000Z 46.5N 43.8W 60 KT 70 MPH 36H 18/1200Z 50.5N 38.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 19/0000Z 52.5N 35.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 20/0000Z 53.5N 31.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 21/0000Z...DISSIPATED $$ Forecaster Pasch

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Hurricane Gert Forecast Discussion Number 16

2017-08-16 22:33:40| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Aug 16 2017 000 WTNT43 KNHC 162033 TCDAT3 Hurricane Gert Discussion Number 16 NWS National Hurricane Center Miami FL AL082017 500 PM AST Wed Aug 16 2017 Cloud tops with temperatures colder than -65 deg C have wrapped almost entirely around Gert's center, although eye temperatures have been fluctuating all day. Dvorak intensity estimates vary widely, from T4.5 from TAFB to around T5.5 from the UW-CIMSS ADT, and since a warm eye has been unable to persist for an extended period of time, the initial intensity is raised conservatively to 85 kt. This makes Gert the first category 2 hurricane of the season. The window of opportunity for additional strengthening appears to be closing. Gert will be moving over the colder waters north of the Gulf Stream in about 12-18 hours, and southwesterly shear will be increasing to well over 30 kt in about 12 hours. Therefore, a fast weakening trend is forecast to begin on Thursday, with Gert becoming a tropical storm by 36 hours. The FSU phase-space diagrams indicate that Gert should be extratropical just after 36 hours, and the GFS, ECMWF, and UKMET all have the cyclone being absorbed by a larger extratropical low over the north Atlantic by day 4. Acceleration continues with the initial motion now 055/27 kt. With Gert firmly embedded within the mid-latitude westerlies, the hurricane's forward speed should increase for the next 24 hours, followed by some deceleration as the cyclone begins to interact with a large cut-off low moving east of Atlantic Canada. Most of the track guidance is a little faster on this cycle, although the ECMWF is significantly slower. The new NHC forecast is nudged a little faster from 12-48 hours, but not too fast given the latest ECMWF solution. The post-tropical portion of the track, intensity, and wind radii forecasts incorporate guidance from NOAA's Ocean Prediction Center. Swells from Gert are affecting portions of the mid-Atlantic coast of the United States, and are expected to spread northward to New England and Atlantic Canada during the next day or two. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local weather forecast office for more information. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 38.7N 62.4W 85 KT 100 MPH 12H 17/0600Z 40.7N 56.9W 85 KT 100 MPH 24H 17/1800Z 44.3N 48.2W 70 KT 80 MPH 36H 18/0600Z 48.3N 40.4W 55 KT 65 MPH 48H 18/1800Z 51.6N 35.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 19/1800Z 54.3N 32.6W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 20/1800Z...ABSORBED BY A LARGER EXTRATROPICAL LOW $$ Forecaster Berg

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Hurricane Gert Forecast Discussion Number 15

2017-08-16 16:36:39| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Aug 16 2017 000 WTNT43 KNHC 161436 TCDAT3 Hurricane Gert Discussion Number 15 NWS National Hurricane Center Miami FL AL082017 1100 AM AST Wed Aug 16 2017 GOES-16 1-minute visible imagery has shown Gert's eye coming and going over the past several hours, and for the first time a distinct warm spot has appeared in infrared images. However, subjective Dvorak estimates are unchanged from six hours ago, and the objective ADT has actually decreased a bit. The initial intensity is therefore held at 80 kt. Gert has another 18-24 hours before it reaches significantly colder waters north of the Gulf Stream, so the cyclone still has the opportunity for a little more strengthening later today and this evening. Southwesterly shear is expected to begin increasing tonight, and the higher shear and colder water should cause a steady weakening trend to begin on Thursday. The global model fields indicate that Gert should be fully extratropical, embedded in a frontal zone, within 48 hours, and that is reflected in the official forecast. There is still a lot of uncertainty regarding when Gert will be absorbed by another larger extratropical cyclone, but most of the guidance tends to agree that it should be absorbed by day 5 over the north Atlantic. Gert's forward speed continues to increase, and the hurricane is now moving toward the northeast with a motion of 055/22 kt. Gert is embedded in mid-latitude westerly flow between a mid-level high centered east of Bermuda and a large cut-off low over eastern Canada, and this pattern should force the cyclone on a fast northeastward pace over the north Atlantic at least for the next 72 hours. A slower motion is forecast by day 4 once post-tropical Gert interacts with the large cut-off low moving east of Atlantic Canada. There was very little change in the latest track guidance, and no significant deviations from the previous NHC forecast were required on this cycle. The post-tropical portion of the track, intensity, and wind radii forecasts incorporate guidance from NOAA's Ocean Prediction Center. Swells from Gert are affecting portions of the mid-Atlantic coast of the United States, and are expected to spread northward to New England and Atlantic Canada during the next day or two. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local weather forecast office for more information. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 37.4N 65.7W 80 KT 90 MPH 12H 17/0000Z 39.0N 61.3W 85 KT 100 MPH 24H 17/1200Z 41.8N 53.6W 75 KT 85 MPH 36H 18/0000Z 45.5N 45.2W 65 KT 75 MPH 48H 18/1200Z 49.5N 38.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 19/1200Z 55.0N 32.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 20/1200Z 55.0N 26.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 21/1200Z...ABSORBED BY A LARGER EXTRATROPICAL LOW $$ Forecaster Berg

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Hurricane Gert Forecast Discussion Number 14

2017-08-16 10:34:40| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Aug 16 2017 000 WTNT43 KNHC 160834 TCDAT3 Hurricane Gert Discussion Number 14 NWS National Hurricane Center Miami FL AL082017 500 AM AST Wed Aug 16 2017 Gert has strengthened a little more during the last several hours. There have been some hints of an eye in infrared satellite images overnight, and the center is embedded beneath a large area of cold cloud tops. The latest Dvorak classifications are both 4.5/77 kt from TAFB and SAB, and recent ADT values are a little higher. Based on these estimates, the initial wind speed is nudged upward to 80 kt. The hurricane is forecast to strengthen a little more during the next 12 to 24 hours while it remains over the warm waters of the Gulf Stream and in a favorable upper-level wind pattern. After that time, sharply colder waters, a significant increase in west- southwesterly shear, and drier air should end the strengthening trend and cause weakening. The models are in good agreement in showing Gert losing its tropical characteristics in 36 to 48 hours. The NHC intensity forecast is largely an update of the previous one. Gert continues to pick up speed, and it is now moving northeastward at 18 kt. The hurricane is located between a subtropical ridge to its southeast and a large deep-layer low pressure system to its northwest. Gert is expected to turn to the east-northeastward and accelerate some more during the next couple of days while it becomes embedded in the fast mid-latitude flow. Beyond a couple of days, when Gert is post-tropical, the system is forecast to slow down and move more erratically while it interacts and ultimately merges with another extratropical low. The NHC track forecast lies closest to the various consensus aids. The post-tropical portion of the track, intensity, and wind radii forecasts are based on guidance provided by NOAA's Ocean Prediction Center. Swells from Gert are beginning to reach portions of the mid-Atlantic coast of the United States, and are expected to spread northward to New England and Atlantic Canada during the next couple of days. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local weather forecast office for more information. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 36.0N 68.4W 80 KT 90 MPH 12H 16/1800Z 37.7N 64.8W 85 KT 100 MPH 24H 17/0600Z 40.0N 58.2W 85 KT 100 MPH 36H 17/1800Z 43.2N 50.1W 75 KT 85 MPH 48H 18/0600Z 47.0N 42.6W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 19/0600Z 54.0N 33.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 20/0600Z 55.5N 27.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 21/0600Z 57.5N 12.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi

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Hurricane Gert Forecast Discussion Number 13

2017-08-16 04:34:07| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Tue Aug 15 2017 000 WTNT43 KNHC 160233 TCDAT3 Hurricane Gert Discussion Number 13 NWS National Hurricane Center Miami FL AL082017 1100 PM EDT Tue Aug 15 2017 Gert looked a bit ragged in satellite imagery earlier this evening, with the eye disappearing and microwave data showing the center to be in the northwest portion of the convective mass. Since then, the cloud pattern has become better organized, with a well-defined convective band now present around the center. Satellite intensity estimates from TAFB and SAB have increased to 77 kt, and thus the initial intensity is increased to 75 kt. Gert continues to recurve into the westerlies between the subtropical ridge and a baroclinic zone extending from North Carolina to Nova Scotia, and the initial motion is now 035/13. The hurricane should accelerate northeastward during the next 24-48 h, passing well south of the Canadian Maritimes and Atlantic Provinces. After that, the cyclone will then likely slow down and turn more northward by day 4 as it interacts with a large baroclinic low moving eastward from northeast Canada. The track guidance remains tightly clustered, and the new forecast track is little changed from the previous track. Conditions appear conducive for additional strengthening during the next 24 h as Gert remains over warm water and in a light/moderate vertical shear environment. The new intensity forecast raises the peak into to 85 kt, which is on the low side of the intensity guidance. After that time, Gert should move over cooler water and begin to merge with the above-mentioned baroclinic zone. The cyclone is now forecast to become extratropical in 48 h, to persist as an extratropical low through 96 h, and then be absorbed by the baroclinic low by 120 h. As mentioned in the previous advisory, the large-scale models suggest the possibility that Gert may survive as its own entity beyond 96 h, and a 120 h point could be added in later advisories. Swells from Gert should spread northward along the mid-Atlantic coast of the United States during the next few days, with the first impacts expected to occur tonight. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local National Weather Service office. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 34.8N 70.3W 75 KT 85 MPH 12H 16/1200Z 36.3N 67.6W 80 KT 90 MPH 24H 17/0000Z 38.5N 62.2W 85 KT 100 MPH 36H 17/1200Z 41.1N 54.8W 75 KT 85 MPH 48H 18/0000Z 44.9N 46.8W 65 KT 75 MPH...POST-TROP/EXTRATROP 72H 19/0000Z 53.0N 35.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 20/0000Z 55.5N 31.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 21/0000Z...ABSORBED BY EXTRATROPICAL LOW $$ Forecaster Beven

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