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Tropical Storm Theta Forecast Discussion Number 15

2020-11-13 15:56:08| National Hurricane Center (Atlantic)

Issued at 300 PM GMT Fri Nov 13 2020 000 WTNT45 KNHC 131456 TCDAT5 Tropical Storm Theta Discussion Number 15 NWS National Hurricane Center Miami FL AL302020 300 PM GMT Fri Nov 13 2020 Satellite images and microwave data this morning are showing that Theta finally has a more classic appearance of a tropical storm. There is a warming of cloud tops over the center, with a curved band of convection wrapping around the eastern portion of the circulation. The scatterometer overpasses missed the core of the cyclone this morning. However, since the cloud pattern has not degraded since the previous advisory, the intensity is being held at 50 kt for this advisory. Theta is forecast to change little in intensity today as the cyclone continues moving in a low shear zone associated with a mid- to upper-level trough axis. By tomorrow, strong northerly shear is forecast to begin impacting the system while stable air gets entrained into its circulation. As a result, Theta is expected to spin down over the weekend, degenerate to a remnant low on Sunday, and dissipate by the middle of next week. Theta continues to move eastward at around 10 kt, steered by a mid-level ridge extending westward from west Africa to the eastern tropical Atlantic. A turn to the east-southeast along with a gradual slowing of the forward motion is expected later today and continuing through the weekend as the ridge weakens, and mid- to upper level northerly winds impart on the cyclone. Early next week, what remains of Theta are expected to turn northward and then accelerate northeastward as a mid-latitude cyclone passes to the north of the region. The NHC forecast is little changed from the previous one and lies near the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 31.7N 23.8W 50 KT 60 MPH 12H 14/0000Z 31.5N 22.2W 50 KT 60 MPH 24H 14/1200Z 31.3N 20.4W 45 KT 50 MPH 36H 15/0000Z 31.0N 19.1W 45 KT 50 MPH 48H 15/1200Z 31.1N 18.3W 35 KT 40 MPH 60H 16/0000Z 31.3N 18.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 16/1200Z 32.8N 18.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 17/1200Z 37.4N 15.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 18/1200Z...DISSIPATED $$ Forecaster Latto

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Tropical Storm Theta Forecast Discussion Number 14

2020-11-13 09:38:31| National Hurricane Center (Atlantic)

Issued at 900 AM GMT Fri Nov 13 2020 000 WTNT45 KNHC 130838 TCDAT5 Tropical Storm Theta Discussion Number 14 NWS National Hurricane Center Miami FL AL302020 900 AM GMT Fri Nov 13 2020 A fortuitous 0348 UTC AMSR2 microwave pass revealed that Theta's surface center was a little to the north of the previous advisory position. The image also indicated that the coldest brightness temperatures were located in the northeast quadrant which sort of conflicts with the earlier scatterometer data showing the stronger surface winds in the southeast quadrant. More than likely though, these winds are being produced by the pressure gradient of the cyclone and a mid-level ridge to the southeast. Since the cloud pattern has changed little during the past several hours and the subjective satellite intensity estimate from TAFB hasn't either, the initial intensity is held at 50 kt for this advisory. Theta is forecast to change little in intensity during the next 12 hours or so as the cyclone continues moving in a low shear zone associated with a mid- to upper-level trough axis. On Saturday, the trough migrates south of Theta, while strong northerly shear and a more stable air mass intrude from the northwest to north. As a result, Theta is expected to spin down and degenerate to a remnant low on Sunday and dissipate by mid next week. Theta has been moving eastward during the last 12 hours within the mid-level troposphere steering current provided by a mid-level ridge extending westward from west Africa to the eastern tropical Atlantic. The short term motion, however, already appears to be the anticipated to the right of track motion, or toward the east-southeast. Regardless, this general motion along with a reduction in forward speed is forecast during the next couple of days as a more vertically shallow Theta is influenced by the low-level flow. By day 3, the remnants of Theta are expected to turn rather sharply northward and continue in this general motion in response to an approaching deep-layer mid-latitude cyclone from the northeastern Atlantic. The NHC forecast is similar to the previous one through the 72 hour period, then adjusted to the right to align more with the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 31.9N 24.9W 50 KT 60 MPH 12H 13/1800Z 31.7N 23.3W 50 KT 60 MPH 24H 14/0600Z 31.4N 21.3W 45 KT 50 MPH 36H 14/1800Z 31.1N 19.7W 45 KT 50 MPH 48H 15/0600Z 30.9N 18.5W 40 KT 45 MPH 60H 15/1800Z 31.1N 18.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 16/0600Z 32.1N 18.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 17/0600Z 36.0N 17.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 18/0600Z...DISSIPATED $$ Forecaster Roberts

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Post-Tropical Cyclone Eta Forecast Discussion Number 52

2020-11-13 09:34:37| National Hurricane Center (Atlantic)

Issued at 400 AM EST Fri Nov 13 2020 000 WTNT44 KNHC 130834 TCDAT4 Post-Tropical Cyclone Eta Discussion Number 52 NWS National Hurricane Center Miami FL AL292020 400 AM EST Fri Nov 13 2020 While the cyclone is still generating a cluster of strong convection to the northeast of the center, satellite imagery, surface observations and scatterometer data indicate that Eta has merged with a baroclinic zone and become an extratropical cyclone off the southeastern coast of the United States. The scatterometer data showed vectors of 40-50 kt along a front or convergence zone northeast of the center, but these vectors were in the strong convective region and their reliability is uncertain. This, the initial intensity is held at a possibly conservative 40 kt. Eta is forecast to strengthen as a baroclinic low until the system is absorbed by another low pressure area in about 48 h. The initial motion is 060/18. The post-tropical cyclone cyclone should continue this general motion with an increase in forward speed until it is absorbed. This is the last advisory issued by the National Hurricane Center on Eta. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 33.3N 76.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 12H 13/1800Z 35.0N 73.1W 40 KT 45 MPH...POST-TROP/EXTRATROP 24H 14/0600Z 37.9N 66.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 14/1800Z 41.1N 57.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 15/0600Z...ABSORBED BY AN EXTRATROPICAL LOW $$ Forecaster Beven

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Tropical Storm Theta Forecast Discussion Number 13

2020-11-13 03:52:52| National Hurricane Center (Atlantic)

Issued at 300 AM GMT Fri Nov 13 2020 121 WTNT45 KNHC 130252 TCDAT5 Tropical Storm Theta Discussion Number 13 NWS National Hurricane Center Miami FL AL302020 300 AM GMT Fri Nov 13 2020 The structure of Theta has been waxing and waning today with moderate convection attempting to wrap around the center, though the coldest cloud tops have been decaying before wrapping fully around. Earlier, there was a 2222 UTC partial ASCAT-B pass that showed peak winds of 40-45 kt on the south side of Theta. However the highest winds from this instrument the previous two nights were in the southwest quadrant and it is estimated that higher winds may still exist in this quadrant of Theta. For this reason, the latest intensity estimate is only adjusted downward to 50 kt for this advisory. Theta continues to track east at 090/12 kt as the system remains steered by flow along the north side of a mid-level ridge. This ridge is forecast to gradually weaken over the next 24-36 h and Theta is forecast to bend to the east-southeast as the cyclone becomes more influenced by mid-level northerly flow associated with an upstream ridge building to the northwest. After 36 h, Theta is expected to slow down significantly as it becomes a shallow cyclone in light low-level flow. Finally, low-level southerly flow ahead of a mid-latitude cyclone is forecast to steer Theta's remnant low northeastward by the end of the forecast. The track guidance this cycle has shifted a bit southward for the first part of the forecast, and the official NHC track forecast has been adjusted slightly further south, close to the reliable ICVN consensus. Thus far, Theta has been struggling to produce deep convection that has successfully wrapped around its center. While Vertical Wind Shear is forecast to decrease per ECMWF-SHIPS guidance over the next 12-24 h, it remains to be seen if the current degree of instability is enough for Theta to take advantage of the more conducive wind environment. Thereafter, Vertical Wind Shear increases sharply from the north, importing a much more stable environment over Theta. For now, the latest NHC intensity forecast maintains the current 50 kt intensity over the next 24 h with weakening forecasted thereafter, in general agreement with the latest intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 31.7N 26.0W 50 KT 60 MPH 12H 13/1200Z 31.7N 24.2W 50 KT 60 MPH 24H 14/0000Z 31.4N 22.1W 50 KT 60 MPH 36H 14/1200Z 31.0N 20.4W 45 KT 50 MPH 48H 15/0000Z 30.8N 19.2W 40 KT 45 MPH 60H 15/1200Z 30.8N 18.6W 30 KT 35 MPH 72H 16/0000Z 31.2N 18.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 17/0000Z 34.3N 18.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 18/0000Z...DISSIPATED $$ Forecaster Papin/Cangialosi

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Tropical Storm Eta Forecast Discussion Number 51

2020-11-13 03:44:27| National Hurricane Center (Atlantic)

Issued at 1000 PM EST Thu Nov 12 2020 000 WTNT44 KNHC 130244 TCDAT4 Tropical Storm Eta Discussion Number 51 NWS National Hurricane Center Miami FL AL292020 1000 PM EST Thu Nov 12 2020 Satellite images and surface observations indicate that the circulation of Eta is becoming stretched as it interacts with a frontal boundary just to its west. Deep convection is mostly confined to the northern side of the system and in patches associated with its trailing trough. Since buoy 41004 off the South Carolina coast recently reported sustained winds of 37 kt, the initial intensity is nudged up to 40 kt for this advisory. The models show the circulation of Eta continuing to lose definition overnight, and it is possible that the tropical storm will open up into a trough soon. Whatever is left of Eta will merge with the nearby front on Friday, causing it to transition into an extratropical cyclone. The non-tropical low is then forecast to dissipate on Saturday over the north Atlantic. Eta, or its remnants, will likely strengthen slightly before it dissipates on Saturday due to the predicted faster forward speed and baroclinic influences. Eta is moving northeastward at 15 kt. An even faster motion to the northeast is expected until the cyclone dissipates as it moves in the flow ahead of a deep-layer trough. This should take Eta, or its remnants, gradually away from the southeast U.S. coast. Deep-layer moisture partly associated with Eta has spread northward along a frontal boundary across eastern North Carolina and just offshore of the Mid-Atlantic coast. See products from the NOAA Weather Prediction Center and your local National Weather Service office for additional information. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 32.3N 79.0W 40 KT 45 MPH 12H 13/1200Z 33.6N 76.1W 40 KT 45 MPH 24H 14/0000Z 36.1N 70.3W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 14/1200Z 39.3N 62.3W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 15/0000Z...DISSIPATED $$ Forecaster Cangialosi

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