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Tropical Depression TWENTY-E Forecast Discussion Number 1

2015-10-20 16:57:37| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT TUE OCT 20 2015 000 WTPZ45 KNHC 201457 TCDEP5 TROPICAL DEPRESSION TWENTY-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP202015 1000 AM CDT TUE OCT 20 2015 Satellite data indicate that deep convection associated with the area of low pressure a few hundred miles southeast of Puerto Escondido, Mexico, has become sufficiently well organized to designate the system as a tropical depression. The circulation of the low has also become better defined according to an overnight ASCAT pass, though it could still be somewhat elongated to the south. The depression's cloud pattern is characterized by interlocking convective bands, with the estimated low-level center underneath the eastward tip of the western band. A Dvorak intensity estimate of T2.0 from TAFB is used to set the initial intensity at 30 kt. Since the center location uncertainty has been high until very recently, the initial motion estimate is a rather uncertain 280/02. The track guidance is in very good agreement that a mid-level ridge over the Gulf of Mexico with an east-northeast to west-northwest orientation should impart a west-southwestward motion for about 24 hours. A turn toward the west and west-northwest with some increase in forward speed is forecast by 36 hours once the ridge over the Gulf of Mexico shifts eastward. When the cyclone reaches the western edge of ridge around 72 hours, it should turn northwestward. The evolution of a deep longwave trough over the southwestern U.S. and northwestern Mexico is of critical importance to the track forecast after that time as the cyclone nears the southwestern coast of Mexico. There are differences between the models regarding the timing and strength of a shortwave trough dropping into the southwestern U. S. during this period, resulting in increasing spread of the track guidance after 72 hours. The track forecast is close to the multi-model consensus, but it is a little west of the GFS and ECMWF solutions beyond day 3. The large-scale environment around the cyclone is forecast to be quite conducive for intensification during the next few days, with SSTs to above 30 deg C, a rich moisture supply in the lower to middle troposphere, and very light vertical shear. The main limiting factor should be how quickly the cyclone develops enough inner-core organization to potentially rapidly intensify. Prior to landfall, an increase in southwesterly vertical shear and drier air associated with the mid-to upper-level trough to the northwest could result in weakening, with a peak intensity mostly likely between the 72- and 96-hour points. The NHC intensity forecast is above the multi-model consensus and in best agreement with the LGEM output until the forecast landfall. Dissipation is shown after 96 hours, though it could occur sooner over the high terrain of the Sierra Madre Occidental. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 13.3N 94.4W 30 KT 35 MPH 12H 21/0000Z 13.0N 95.5W 35 KT 40 MPH 24H 21/1200Z 12.8N 97.0W 45 KT 50 MPH 36H 22/0000Z 12.9N 98.9W 55 KT 65 MPH 48H 22/1200Z 13.9N 101.0W 70 KT 80 MPH 72H 23/1200Z 16.3N 103.7W 85 KT 100 MPH 96H 24/1200Z 20.5N 104.4W 50 KT 60 MPH...INLAND 120H 25/1200Z...DISSIPATED $$ Forecaster Kimberlain

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Hurricane OLAF Forecast Discussion Number 21

2015-10-20 04:59:33| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON OCT 19 2015 000 WTPZ44 KNHC 200259 TCDEP4 HURRICANE OLAF DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192015 800 PM PDT MON OCT 19 2015 Olaf has maintained a small pinhole eye with a diameter of no more than 10 n mi. Satellite intensity estimates were a consensus T6.0/115 kt from TAFB, UW-CIMSS ADT, and the NHC AODT algorithm at 20/0000Z. However, since that time the eye has warmed a little and a ring of cloud tops colder than -75C has developed around the eye, so the intensity has been nudged slightly higher to 120 kt. The initial motion estimate is 275/09 kt. Olaf is expected to continue moving westward to west-northwestward along the southern periphery of a deep-layer ridge for the next 24 hours or so, and then turn northwestward toward a developing weakness in the ridge on days 2 and 3. By 96 and 120 hours, a series of fast-moving shortwave troughs embedded in the mid-latitude westerlies is expected to gradually create a break in the mid-level ridge between 145W-150W longitude, allowing Olaf to move northward and remain well east of the Hawaiian Islands. The latest NHC model guidance is in much better agreement on this developing scenario compared to 24 hours ago, and even the UKMET model has shifted eastward and is now on the east side of the guidance envelope at 96 and 120 hours. The official forecast track lies a little to the left of the previous advisory track, and follows the consensus models TVCE and GFEX. There has been slight flattening of the CDO in the northwestern quadrant caused by some light to moderate northwesterly mid-level shear as noted in recent UW-CIMSS shear analyses, which could inhibit intensification some in the short term. However, some additional strengthening is still likely over the next day or so since Olaf will be affected by deep-layer shear of 5 kt or less and be over 29C SSTs. As mentioned in the previous advisory, there could be fluctuations in intensity due to eyewall replacement cycles that can not be forecast more than a few hours in advance. The NHC intensity forecast continues to indicate a peak of 125 kt at 12-36 hours, followed by a slow decay by 48-72 as Olaf begins to move slowly over slightly cooler SSTs and into a moderate southwesterly vertical wind shear regime. The official intensity forecast remains above the intensity consensus, but below the LGEM and SHIPS forecasts, which bring Olaf to just below category 5 strength in 36-48 hours. With Olaf moving into the central North Pacific basin within the next six hours or so, this will be the last advisory from NHC. Future information on Olaf can be found in advisories issued by the Central Pacific Hurricane Center beginning at 1100 PM HST (0900Z). FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 10.1N 139.5W 120 KT 140 MPH 12H 20/1200Z 10.4N 140.8W 125 KT 145 MPH 24H 21/0000Z 11.1N 142.4W 125 KT 145 MPH 36H 21/1200Z 12.0N 143.8W 125 KT 145 MPH 48H 22/0000Z 13.0N 145.0W 120 KT 140 MPH 72H 23/0000Z 15.4N 146.6W 105 KT 120 MPH 96H 24/0000Z 18.3N 146.9W 95 KT 110 MPH 120H 25/0000Z 20.9N 146.4W 80 KT 90 MPH $$ Forecaster Stewart

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Hurricane OLAF Forecast Discussion Number 20

2015-10-19 22:32:59| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON OCT 19 2015 000 WTPZ44 KNHC 192032 TCDEP4 HURRICANE OLAF DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192015 200 PM PDT MON OCT 19 2015 Olaf has continued to rapidly intensify today. The hurricane has a classical appearance on satellite imagery with a small, clear eye surrounded by a CDO with cloud tops of -70C to -80C. Dvorak estimates from TAFB and SAB and UW-CIMSS were T6.0/115 kt, and these are the basis for the initial intensity. Olaf has strengthened 45 kt in the last 24 hours, and some additional strengthening is still possible in the next day or two. However, there could also be fluctuations in intensity due to eyewall replacement cycles that are not accounted for here. The new NHC forecast shows a peak of 125 kt at 12 h to 36 h and then a slow decay as the cyclone begins to move over slightly cooler SSTs and into a drier environment later in the period. The official forecast is above the intensity consensus and close to the FSU Superensemble. The initial motion estimate is 275/10, as Olaf continues to move westward to the south of a mid-level ridge centered near 30N/140W. This ridge will gradually weaken as a trough advances over the north-central Pacific, and this will allow Olaf to finally begin gaining some latitude as it gradually turns northwestward and then northward during the forecast period. The UKMET model still is on the left side of the guidance envelope for the first 48 hours, but has shifted toward a sharper northward turn after that time. This puts the GFS and ECMWF now on the left side of the guidance envelope. Overall, the new NHC track forecast is an update of the previous one and is still left of the consensus. The official forecast is between the UKMET and the rest of the guidance in the first 48 hours, and then lies along the left side of the track model envelope at days 3 through 5. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 10.0N 138.7W 115 KT 130 MPH 12H 20/0600Z 10.3N 140.1W 125 KT 145 MPH 24H 20/1800Z 10.9N 141.6W 125 KT 145 MPH 36H 21/0600Z 11.7N 143.1W 125 KT 145 MPH 48H 21/1800Z 12.6N 144.4W 120 KT 140 MPH 72H 22/1800Z 14.7N 146.1W 110 KT 125 MPH 96H 23/1800Z 17.7N 147.0W 100 KT 115 MPH 120H 24/1800Z 20.0N 147.0W 85 KT 100 MPH $$ Forecaster Brennan

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Hurricane OLAF Forecast Discussion Number 19

2015-10-19 16:50:29| National Hurricane Center (East Pacific)

Issued at 800 AM PDT MON OCT 19 2015 000 WTPZ44 KNHC 191450 TCDEP4 HURRICANE OLAF DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192015 800 AM PDT MON OCT 19 2015 A small eye is now apparent in infrared imagery, and the coverage and symmetry of the cold cloud tops has improved during the past few hours. The initial intensity is set to 100 kt based on the latest Dvorak classification of T5.5/102 kt from SAB, making Olaf the 6th major hurricane in the eastern North Pacific this year. This is the farthest south that a major hurricane has formed in the basin since reliable records began in 1971. Further strengthening appears likely in the next day or so, and in fact the SHIPS RI index shows a 44 percent chance of a 25-kt increase in the next 24 hours. The NHC intensity forecast has been adjusted upward to account for the observed strengthening, and shows a peak of 125 kt in 24 hours. Little change in intensity is then shown through 48 hours, however, there could be fluctuations in intensity due to eyewall cycles during this time that are not represented in the forecast. Later in the period, gradual weakening should begin as Olaf moves over slightly cooler waters into a somewhat drier environment. The new NHC forecast is above the guidance in the first 24 hours and close to the latest SHIPS model prediction thereafter. Olaf continues to move westward, with an initial motion of 280/12. This continues a trend of a motion that has been a little faster and to the left of much of the guidance and the NHC forecast. While the track forecast reasoning has not changed, with Olaf expected to gradually turn northward through the forecast period as the ridge to the north erodes, the guidance envelope has continued to shift westward this cycle. In fact, the multi-model consensus has shifted westward by about 2 degrees compared to 24 hours ago at days 4 and 5. The new NHC track forecast has been adjusted to the left this cycle by 60 to 90 n mi at days 2 through 5. The NHC track is now on the left side of the guidance envelope and closer to the UKMET model, which has been the best performing track model so far for Olaf. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 9.9N 137.7W 100 KT 115 MPH 12H 20/0000Z 10.2N 139.1W 115 KT 130 MPH 24H 20/1200Z 10.8N 140.8W 125 KT 145 MPH 36H 21/0000Z 11.4N 142.4W 120 KT 140 MPH 48H 21/1200Z 12.2N 144.0W 120 KT 140 MPH 72H 22/1200Z 14.0N 146.0W 110 KT 125 MPH 96H 23/1200Z 16.7N 146.9W 100 KT 115 MPH 120H 24/1200Z 19.5N 147.5W 85 KT 100 MPH $$ Forecaster Brennan

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Hurricane OLAF Forecast Discussion Number 18

2015-10-19 10:42:26| National Hurricane Center (East Pacific)

Issued at 200 AM PDT MON OCT 19 2015 000 WTPZ44 KNHC 190842 TCDEP4 HURRICANE OLAF DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192015 200 AM PDT MON OCT 19 2015 The overall satellite presentation of the hurricane has not changed since the previous advisory. The ragged eye that was seen in the last few visible satellite pictures has not become apparent in overnight infrared images, but recent microwave data have indicated the presence of a small well-defined eye. Objective and subjective Dvorak satellite intensity estimates still support an initial wind speed of 85 kt. Olaf is expected to remain over warm water and in a low vertical wind shear environment during the next several days. These factors favor intensification and Olaf is expected to become a major hurricane during the next 12 to 24 hours. After that time, some additional strengthening is forecast, but fluctuations in intensity are likely due to eyewall cycles. The new NHC forecast is unchanged from the previous advisory and is near the upper-end of the intensity guidance, closest to the SHIPS/LGEM models. Some gradual weakening is shown at days 4 and 5 when Olaf moves over slightly cooler waters and into an area of drier mid-level air. Recent satellite and microwave fixes show that Olaf is moving westward or 280/10 kt. The track forecast reasoning remains unchanged, as Olaf is expected to move around the southwestern and western portions of a deep-layer subtropical ridge during the next several days. The hurricane is forecast to turn west- northwestward later today before it moves into the Central Pacific basin tonight. A northwestward motion is expected in 2 to 3 days, and a turn toward the north should occur late in the period when Olaf nears a break in the ridge along 145W. The new NHC track is similar to the previous advisory through 72 hours, but has been adjusted westward at days 4 and 5 to be closer to the latest multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 10.0N 136.4W 85 KT 100 MPH 12H 19/1800Z 10.3N 137.8W 95 KT 110 MPH 24H 20/0600Z 10.8N 139.6W 105 KT 120 MPH 36H 20/1800Z 11.4N 141.1W 110 KT 125 MPH 48H 21/0600Z 12.3N 142.5W 110 KT 125 MPH 72H 22/0600Z 14.3N 144.8W 110 KT 125 MPH 96H 23/0600Z 16.5N 146.0W 100 KT 115 MPH 120H 24/0600Z 19.0N 146.0W 85 KT 100 MPH $$ Forecaster Brown

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