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Tropical Storm AMANDA Forecast Discussion Number 5

2014-05-23 22:33:11| National Hurricane Center (East Pacific)

Issued at 200 PM PDT FRI MAY 23 2014 000 WTPZ41 KNHC 232032 TCDEP1 TROPICAL STORM AMANDA DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 200 PM PDT FRI MAY 23 2014 Visible and microwave imagery suggest that Amanda's low- and mid-level circulation centers may be offset from each other due to some southerly shear, as analyzed by UW-CIMSS. However, convective banding continues to increase, and overall the system is taking on a more circular appearance. Dvorak estimates from TAFB and SAB have risen to T2.5/35 kt, and the initial intensity is held at 35 kt for this advisory. With relatively light shear and sea surface temperatures around 29C, Amanda is forecast to continue strengthening at least for the next 3 days or so. The intensity guidance has trended upward, and the LGEM and HWRF have now come in line with the SHIPS and GFDL models by showing Amanda reaching hurricane status in a few days. The SHIPS RI index continues to run high, and several of the models suggest that Amanda could reach hurricane strength by 36 hours. The NHC intensity forecast has been bumped upward, but further modifications may be required in future advisories if faster intensification appears to be setting in. Amanda is moving slowly around the southwestern side of a weak mid-level anticyclone centered over Mexico, and the initial motion is 290/3 kt. With the anticyclone expected to weaken further, Amanda is likely to creep west-northwestward for the next 2 to 3 days. The global models indicate that a mid-level low will form along 130W by day 3, and that feature should help turn Amanda toward the north at a slightly faster speed by the end of the forecast period. With the exception of the HWRF model, the remainder of the track guidance agrees on this slow northward turn. The track guidance envelope has contracted a bit, and no significant changes to the previous NHC track were required. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 11.0N 108.8W 35 KT 40 MPH 12H 24/0600Z 11.2N 109.2W 45 KT 50 MPH 24H 24/1800Z 11.6N 110.1W 50 KT 60 MPH 36H 25/0600Z 11.8N 110.8W 60 KT 70 MPH 48H 25/1800Z 12.0N 111.2W 65 KT 75 MPH 72H 26/1800Z 12.5N 111.5W 70 KT 80 MPH 96H 27/1800Z 14.0N 112.0W 65 KT 75 MPH 120H 28/1800Z 15.5N 112.0W 50 KT 60 MPH $$ Forecaster Berg

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Tropical Storm AMANDA Forecast Discussion Number 4

2014-05-23 16:57:05| National Hurricane Center (East Pacific)

Issued at 800 AM PDT FRI MAY 23 2014 000 WTPZ41 KNHC 231456 TCDEP1 TROPICAL STORM AMANDA DISCUSSION NUMBER 4...RETRANSMITTED NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 800 AM PDT FRI MAY 23 2014 Convection has been gradually filling in near the center and taking on a more pronounced banding structure during the past few hours. Dvorak estimates from TAFB and SAB were T2.0/30 kt at 1200 UTC, but the most recent UW-CIMSS ADT estimates are running around 40 kt. In addition, recent AMSU intensity estimates yielded 38 kt and 44 kt. Based on the higher objective numbers, and the overall increase in convective organization since 1200 UTC, the depression is being upgraded to Tropical Storm Amanda at this time. The initial intensity is set at 35 kt based on a consensus of the subjective and objective numbers. Amanda's initial motion is a slow 295/4 kt. The storm is located to the southwest of a fairly weak mid-level anticyclone over central Mexico and to the south of a large deep-layer low over southern California. The anticyclone is forecast to weaken during the next couple of days, while the deep-layer low slides almost due eastward across the southwestern U.S. As a result, Amanda is expected to remain in weak steering flow, and its motion should remain less than 5 kt during the next 5 days. Amanda is now expected to turn northward by day 5 due to mid-level ridging redeveloping over Mexico and a mid-level low forming near 130W. The GFS has had the most dramatic shift in track since yesterday and now shows Amanda turning northward by the end of the forecast period. The updated NHC forecast has been shifted a bit to the right of the previous one now that there is a little more agreement among the models on a northward turn. Amanda is expected to remain in a relatively light-shear environment for the next 3 days or so, and therefore at least gradual strengthening is anticipated. Although upwelling of cold water could be a concern due to Amanda's slow forecast motion, upper ocean heat content is expected to increase along the cyclone's path. Due to these favorable conditions, the SHIPS RI index still supports a significant potential (about a 50 percent chance of a 25-kt increase over the next 24 hours) of rapid intensification. All of the models have been trending toward a higher peak intensity, led by the SHIPS and GFDL, which both make Amanda a hurricane by 48 hours. The new NHC forecast is not quite that aggressive, but it does now show Amanda reaching hurricane strength in about 3 days or so. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 10.9N 108.4W 35 KT 40 MPH 12H 24/0000Z 11.1N 108.9W 40 KT 45 MPH 24H 24/1200Z 11.5N 109.7W 45 KT 50 MPH 36H 25/0000Z 11.7N 110.3W 50 KT 60 MPH 48H 25/1200Z 11.9N 110.8W 55 KT 65 MPH 72H 26/1200Z 12.5N 111.5W 65 KT 75 MPH 96H 27/1200Z 13.5N 112.0W 65 KT 75 MPH 120H 28/1200Z 15.0N 112.0W 60 KT 70 MPH $$ Forecaster Berg

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Tropical Depression ONE-E Forecast Discussion Number 3

2014-05-23 10:44:32| National Hurricane Center (East Pacific)

Issued at 200 AM PDT FRI MAY 23 2014 000 WTPZ41 KNHC 230844 TCDEP1 TROPICAL DEPRESSION ONE-E DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 200 AM PDT FRI MAY 23 2014 Convective banding is currently increasing near the center of Tropical Depression One-E over the northern semicircle. There have been multiple recent scatterometer overpasses, with recent ASCAT-A data showing an area of 25-30 kt winds about 60-75 n mi from the center over the northeastern quadrant. Based on this, the initial intensity is increased to 30 kt. The cirrus outflow is good in all directions. However, analyses from CIMSS at the University of Wisconsin suggest some light southerly shear continues to affect the system. The scatterometer fixes have helped pin down the center location, and the initial motion is estimated at 295/4. The depression is south of a break in the subtropical ridge caused by a deep-layer trough over the western United States. While the large-scale models forecast this trough to move eastward, the subtropical ridge is likely to remain weak with the tropical cyclone remaining in an area of light steering currents for most of the forecast period. While the guidance shows a large spread, there is general agreement that the depression should move slowly west-northwestward for the next 2-3 days, followed by a turn to the north as a mid/upper-level trough develops near 120W and a mid/upper-level ridge develops east of the cyclone. The new forecast track is near the previous track through 72 hour and is nudged a little to the east of the previous track after that time. The track lies north of the model consensus through 72 hours and west of the consensus at 96 and 120 hours. The depression is currently expected to be in an area of light/ moderate southerly vertical wind shear during the forecast period. This should allow at least gradual strengthening, and the new intensity forecast is similar to the previous forecast and the intensity consensus. There are two potential, and contradictory, issues with the intensity forecast. The first is that the large-scale models forecast moderate to strong upper-level winds near the cyclone during the forecast period, especially after 72 hours. If these winds get closer to the system than currently forecast, they could inhibit development. The second is that the SHIPS rapid intensification index is showing a significantly above- normal chance of rapid intensification, and the GFDL model forecasts the depression to reach hurricane strength in about 72 hours. If the stronger upper-level wind do not impact the cyclone, it could strengthen more than currently forecast. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 10.8N 108.2W 30 KT 35 MPH 12H 23/1800Z 11.1N 108.8W 35 KT 40 MPH 24H 24/0600Z 11.3N 109.4W 40 KT 45 MPH 36H 24/1800Z 11.5N 110.0W 45 KT 50 MPH 48H 25/0600Z 11.6N 110.5W 50 KT 60 MPH 72H 26/0600Z 12.0N 111.5W 55 KT 65 MPH 96H 27/0600Z 12.5N 112.0W 60 KT 70 MPH 120H 28/0600Z 13.5N 112.5W 60 KT 70 MPH $$ Forecaster Beven

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Tropical Depression ONE-E Forecast Discussion Number 2

2014-05-23 04:38:00| National Hurricane Center (East Pacific)

Issued at 800 PM PDT THU MAY 22 2014 000 WTPZ41 KNHC 230237 TCDEP1 TROPICAL DEPRESSION ONE-E DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 800 PM PDT THU MAY 22 2014 The convective appearance of the depression is somewhat disheveled this evening, as the coldest cloud tops are located north and east of the estimated center position. The initial intensity is held at 25 kt based on the latest Dvorak estimate from SAB. The satellite presentation, satellite analyses from UW-CIMSS, and the SHIPS model suggest that some southerly and westerly shear associated with a mid/upper-level trough well to the north is currently affecting the cyclone. During the next day or so, this environment should support only gradual intensification. As the trough moves away the shear should decrease, which should allow for more strengthening later in the period while the cyclone is over warm waters. The NHC intensity forecast is similar to the previous one through 72 hours, and has been adjusted upward toward the IVCN intensity consensus after that time, and is close to a blend of the SHIPS and LGEM models. The center of the depression has been difficult to locate with geostationary and microwave imagery. However, a blend of satellite fixes and continuity yields an initial motion of 290/04. The cyclone is expected to move slowly west-northwestward for the next couple of days, as a mid-level ridge to the east weakens and the trough north of the depression moves eastward. Through 48 hours the new official forecast is a little faster than the previous one and is close to a blend of the GFS and ECMWF models. Later in the period much of the guidance has shifted northward, with the GFS, GEFS ensemble mean, and GFDL taking the cyclone sharply poleward by day 5 as a ridge rebuilds to the east. The HWRF also shows a northward turn but is slower, while the ECMWF shows a much slower motion farther to the east of the rest of the guidance. Given the large shift in the guidance this cycle, only small adjustments have been made to the NHC forecast late in the period. The NHC track is close to the previous one at days 3 and 4, and has been adjusted a little to the north and east at day 5, but remains well south of the multi-model consensus at that time. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 10.6N 107.8W 25 KT 30 MPH 12H 23/1200Z 10.8N 108.3W 35 KT 40 MPH 24H 24/0000Z 11.1N 109.0W 40 KT 45 MPH 36H 24/1200Z 11.4N 109.6W 45 KT 50 MPH 48H 25/0000Z 11.6N 110.0W 50 KT 60 MPH 72H 26/0000Z 11.8N 110.6W 55 KT 65 MPH 96H 27/0000Z 12.0N 111.5W 60 KT 70 MPH 120H 28/0000Z 12.5N 112.5W 60 KT 70 MPH $$ Forecaster Brennan

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Tropical Depression ONE-E Forecast Discussion Number 1

2014-05-22 23:01:30| National Hurricane Center (East Pacific)

Issued at 200 PM PDT THU MAY 22 2014 000 WTPZ41 KNHC 222101 TCDEP1 TROPICAL DEPRESSION ONE-E DISCUSSION NUMBER 1...CORRECTED NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 200 PM PDT THU MAY 22 2014 Corrected wording in third paragraph discussing SHIPS RI index. Deep convection associated with an area of low pressure well to the southwest of Mexico has gradually become better organized during the past 12 to 24 hours, and a 1708 UTC ASCAT-B pass indicated that the system has a sufficiently well-defined center. Therefore, advisories are being initiated on the first tropical depression of the eastern North Pacific season. The initial intensity is set at 25 kt based on the ASCAT data and satellite estimates of T1.5 from both TAFB and SAB. The depression has been moving slowly toward the west-northwest while located on the edge of a mid-level ridge extending west from Mexico, and the initial motion estimate is 285/3 kt. The depression is expected to remain just to the west of the ridge and to the south of a deep-layer cyclone centered over California, which will likely keep it in a weak steering environment for the next 3 to 4 days. In fact, the ECMWF model even shows the depression becoming nearly stationary or meandering for a few days due to the weak steering. The official forecast shows a relatively slow track toward the west-northwest during the next 5 days and is close to the model consensus TVCE. The depression is embedded in an environment of light vertical shear, which will likely support at least gradual intensification during the next few days. There is some disagreement among the intensity models as to how much strengthening will occur, however. For example, the statistical LGEM keeps the depression below tropical storm strength for about 48 hours. On the other hand, the SHIPS RI index indicates a 42 percent chance of a 25-kt increase in winds within the next 24 hours. With the RI index relatively high, the official forecast is higher than the LGEM for the first few days. By days 4 and 5, vertical shear is expected to strengthen, and the intensity is forecast to level off or decrease by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 10.3N 107.4W 25 KT 30 MPH 12H 23/0600Z 10.5N 108.0W 35 KT 40 MPH 24H 23/1800Z 10.8N 108.6W 40 KT 45 MPH 36H 24/0600Z 11.1N 109.2W 45 KT 50 MPH 48H 24/1800Z 11.4N 109.7W 50 KT 60 MPH 72H 25/1800Z 11.7N 110.3W 55 KT 65 MPH 96H 26/1800Z 12.0N 111.0W 55 KT 65 MPH 120H 27/1800Z 12.0N 113.0W 50 KT 60 MPH $$ Forecaster Berg

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