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Hurricane JIMENA Forecast Discussion Number 11

2015-08-29 10:52:48| National Hurricane Center (East Pacific)

Issued at 200 AM PDT SAT AUG 29 2015 000 WTPZ43 KNHC 290852 TCDEP3 HURRICANE JIMENA DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 200 AM PDT SAT AUG 29 2015 Jimena is an impressive hurricane on satellite imagery tonight with a symmetric central dense overcast, warm eye, and fanning cirrus outflow in all quadrants. The current intensity estimate is 130 kt, a blend of the latest Dvorak values from TAFB, SAB and UW-CIMSS. While large-scale environmental factors are still favorable for further strengthening this weekend, Jimena will likely go through an eyewall replacement cycle during the next day or so, which can cause fluctuations in intensity that are impossible to forecast. However, Jimena is likely to remain a very powerful hurricane for the next several days. A slow decay is forecast by late Sunday since oceanic and atmospheric conditions will only gradually become less conducive, with a more pronounced weakening expected by mid-week. The new forecast is primarily a blend of the previous one and the statistical models in the first two days, with a heavier weight on the intensity consensus at days 3 to 5. The initial motion estimate is 270/8. Jimena's heading should become west-northwestward later today and continue in that general direction for the next several days while it moves around the subtropical ridge. As Jimena nears a break in the ridge around 140W, a significant decrease in forward speed is likely after 96 hours. The track guidance remains tightly clustered, and the new track forecast has been moved only slightly southward, similar to the adjustment made on the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 12.3N 124.8W 130 KT 150 MPH 12H 29/1800Z 12.5N 126.2W 135 KT 155 MPH 24H 30/0600Z 13.3N 128.2W 140 KT 160 MPH 36H 30/1800Z 14.2N 130.3W 135 KT 155 MPH 48H 31/0600Z 15.0N 132.8W 130 KT 150 MPH 72H 01/0600Z 16.2N 137.2W 120 KT 140 MPH 96H 02/0600Z 17.0N 140.0W 100 KT 115 MPH 120H 03/0600Z 17.7N 141.5W 85 KT 100 MPH $$ Forecaster Blake

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Hurricane JIMENA Forecast Discussion Number 10

2015-08-29 04:49:44| National Hurricane Center (East Pacific)

Issued at 800 PM PDT FRI AUG 28 2015 000 WTPZ43 KNHC 290249 TCDEP3 HURRICANE JIMENA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 800 PM PDT FRI AUG 28 2015 Jimena is rapidly intensifying. Conventional satellite imagery shows that the hurricane's well-defined eye has warmed and contracted since the last advisory. Its central dense overcast, consisting of very cold cloud top temperatures, has also become increasingly more symmetric. Aside from Jimena's core features, outer bands surrounding the cyclone have also increased and become better defined. Dvorak classifications were T5.5/102 kt from TAFB and SAB at 0000 UTC and the latest UW-CIMSS ADT value is 6.2/120 kt. A blend of these data are used to arrive at an intensity estimate of 110 kt, making Jimena the fourth major hurricane of the season. The initial motion estimate is 275/10, although the cyclone appears to have recently experienced a southward trochoidal wobble. Directly underneath a subtropical ridge to the north, Jimena should maintain a general westward course for the next 12 to 24 hours. After that time, Jimena's heading should become west-northwestward as it nears a break in this ridge around 140W, created by a mid-level trough extending southwestward from California. A significant decrease in forward speed is likely after 96 hours when the cyclone reaches the weakness around 140W. The track guidance is tightly clustered through 3 days and is only slightly divergent after that time, with the multi-model consensus trending southward during the last 24 hours from days 3 to 5. The new track forecast has been nudged slightly southward in the short term and a little bit more in the extended range, following the trend in the guidance. The rapid intensification phase that Jimena is undergoing is likely to continue in the short term while it encounters relatively light shear and moves over anomalously high oceanic heat content. These very conducive large-scale factors for intensification suggest that Jimena should reach a peak intensity of near category 5 strength in about 24 hours or so. The hurricane could remain around its peak intensity through 48 hours, even though SHIPS model output shows some drying of the lower to middle troposphere along Jimena's track. However, it should be noted that intense hurricanes such as Jimena frequently experience eyewall replacements that can cause fluctuations in intensity, and their occurrence and evolution are nearly impossible to predict. After about 2 days, a slow decay is forecast since oceanic and atmospheric conditions will only gradually become less conducive. Jimena's continued strenghtening has required an upward adjustment of the intensity forecast in the short term, and the new forecast is in excellent agreement with the statistical guidance as well as the FSU Superensemble output. The new forecast then trends toward the multi-model consensus from days 3 to 5. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 12.3N 124.2W 110 KT 125 MPH 12H 29/1200Z 12.5N 125.5W 125 KT 145 MPH 24H 30/0000Z 13.0N 127.4W 135 KT 155 MPH 36H 30/1200Z 13.9N 129.5W 130 KT 150 MPH 48H 31/0000Z 14.9N 131.9W 125 KT 145 MPH 72H 01/0000Z 16.3N 136.6W 115 KT 130 MPH 96H 02/0000Z 17.3N 139.8W 100 KT 115 MPH 120H 03/0000Z 18.0N 141.7W 85 KT 100 MPH $$ Forecaster Kimberlain

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Tropical Storm ERIKA Forecast Discussion Number 17

2015-08-29 04:48:17| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT FRI AUG 28 2015 000 WTNT45 KNHC 290248 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 1100 PM EDT FRI AUG 28 2015 Dropsondes from the NOAA P3 flying around Hispaniola were very helpful in locating the mean center of the broad circulation associated with Erika, which is moving over the high terrain of Hispaniola. There is plenty of deep convection associated with the cyclone, and gusts to tropical storm force are being reported in Barahona, on the south coast of the Dominican Republic. Given that the circulation is interacting with land, the initial intensity has been set at 40 kt. Erika is fighting both land and a hostile wind shear environment, and it will be very difficult for the cyclone to recover. Consequently, weakening in the short term is indicated in the NHC forecast, and there is a strong likelihood that Erika will degenerate to a tropical wave during its interaction with land. However, if it survives, there is a very small opportunity for Erika to regain tropical storm strength in the Florida Straits and the southeastern Gulf of Mexico, where the environment is less hostile. It is interesting to note, and to remember, the fact that most of the state-of-the art dynamical models were forecasting Erika to become a strong hurricane up to yesterday, and today basically dissipate the cyclone. The initial motion is uncertain, and the best estimate is toward the west-northwest or 285 degrees at 17 kt. It seems that Erika has changed very little in forward speed since its formation. However, the cyclone is reaching the southwestern edge of the subtropical ridge and the steering currents are weaker. Therefore, Erika is forecast to slow down and turn to the northwest in about two days. Once in the eastern Gulf of Mexico, a more northerly track is anticipated. There is not much track guidance available tonight since most of the models lose the circulation of Erika, and the NHC forecast is following the weak perturbation observed in the model fields. The greatest short-term threat posed by Erika continues to be very heavy rainfall over portions of Hispaniola and eastern Cuba. These rains could produce flash floods and mudslides. We must emphasize that although this would normally be an appropriate time for a tropical storm watch for portions of southern Florida, following typical timelines, we have elected to wait until we see if Erika survives after it passes Hispaniola. There is a significant chance that no watches or warnings for Florida will be required. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 18.5N 72.9W 40 KT 45 MPH...INLAND 12H 29/1200Z 20.0N 75.0W 35 KT 40 MPH...INLAND 24H 30/0000Z 22.0N 78.0W 30 KT 35 MPH...INLAND 36H 30/1200Z 23.5N 80.5W 30 KT 35 MPH...OVER WATER 48H 31/0000Z 25.0N 82.0W 35 KT 40 MPH 72H 01/0000Z 26.5N 83.0W 35 KT 40 MPH 96H 02/0000Z 28.5N 84.0W 40 KT 45 MPH 120H 03/0000Z 31.0N 84.0W 25 KT 30 MPH...INLAND $$ Forecaster Avila

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Tropical Storm ERIKA Forecast Discussion Number 16

2015-08-28 22:55:15| National Hurricane Center (Atlantic)

Issued at 500 PM EDT FRI AUG 28 2015 000 WTNT45 KNHC 282055 TCDAT5 TROPICAL STORM ERIKA DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052015 500 PM EDT FRI AUG 28 2015 The low-level center of Erika continues to be be located west of the convection due to the impact of 25-30 kt of westerly vertical wind shear. Satellite imagery and reports from an Air Force Reserve Hurricane Hunter aircraft indicate that the circulation has been losing definition during the day and it is now barely closed, at best. However, clusters of strong convection continue in the eastern semicircle, and the initial intensity is held at 45 kt on the premise that the strong winds observed earlier are still present. The central pressure of 1009 mb is based on observations from the Dominican Republic. Erika has been moving more westward for the past several hours and the initial motion is 280/17. There is no change to the forecast philosophy from the previous advisory. A generally west- northwestward to northwestward motion is expected for the next 48 hours or so as Erika moves around the southwestern periphery of the subtropical ridge. After that time, a northwestward and northward turn and a decrease in forward speed are forecast as Erika moves between the ridge and a mid- to upper-level trough over the Gulf of Mexico. While the track guidance is generally in good agreement, it should be noted that the guidance has been consistently forecasting a west-northwestward turn that has so far failed to occur. On the other hand, there is still a chance for a center to re-form farther to the north during the passage over Hispaniola. So while the forecast track has been shifted west of the previous advisory, it still lies near the northern edge of the guidance envelope for the first 48 hours to maintain some continuity with the previous forecast. Additional adjustments may be necessary depending on how Erika evolves during the next 12-18 hours. The forecast intensity has been significantly changed to show a much weaker cyclone, with Erika now forecast to become a tropical depression in about 24 hours, followed by some slight intensification at 48 and 72 hours. This represents a compromise between two scenarios. The first is the increasing likelihood that Erika will degenerate to a tropical wave during the passage over Hispaniola, a scenario supported by the GFS, UKMET, and ECMWF models. The second acknowledges that the shear is still expected to subside after 36 hours and we're are not quite prepared to rule out tropical storm impacts in Florida. The SHIPS and LGEM support this possibility. The greatest short-term threat posed by Erika continues to be very heavy rainfall over portions of the Dominican Republic and Haiti today and tonight. These rains could produce flash floods and mud slides. Although this would normally be an appropriate time for a tropical storm watch for portions of southern Florida, following typical timelines, we have elected to wait until we see what's left of Erika after it passes Hispaniola. There is a significant chance that no watches or warnings for Florida will be required. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 17.9N 71.2W 45 KT 50 MPH 12H 29/0600Z 19.5N 73.5W 40 KT 45 MPH 24H 29/1800Z 21.3N 76.5W 30 KT 35 MPH...INLAND 36H 30/0600Z 22.7N 79.3W 30 KT 35 MPH...OVER WATER 48H 30/1800Z 24.0N 81.0W 35 KT 40 MPH 72H 31/1800Z 27.0N 82.5W 35 KT 40 MPH 96H 01/1800Z 29.0N 82.5W 30 KT 35 MPH...INLAND 120H 02/1800Z 31.0N 82.5W 25 KT 30 MPH...INLAND $$ Forecaster Beven

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Hurricane JIMENA Forecast Discussion Number 9

2015-08-28 22:31:48| National Hurricane Center (East Pacific)

Issued at 200 PM PDT FRI AUG 28 2015 000 WTPZ43 KNHC 282031 TCDEP3 HURRICANE JIMENA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132015 200 PM PDT FRI AUG 28 2015 A distinct eye cleared out in both visible and infrared satellite imagery around 1800 UTC, and convective cloud tops surrounding the eye are as cold as -75 degrees Celsius. Dvorak intensity estimates were T5.0/90 kt from TAFB and T4.5/77 kt from SAB at 1800 UTC, and the most recent UW-CIMSS ADT estimate is T5.4/100 kt. The initial intensity is therefore raised to 90 kt on this advisory. Jimena continues to rapidly intensify, with the intensity having increased by 35-40 kt in the past 24 hours. The environment near Jimena remains conducive for further strengthening. Low shear and very warm ocean water could allow rapid intensification to continue, and the SHIPS Rapid Intensification Index is showing a 43 percent chance of a 30-kt increase in intensity during the next 24 hours. Based on the latest statistical-dynamical guidance, a peak in intensity is likely to occur between 36 and 48 hours. After that time, a slightly drier air mass and decreasing oceanic heat content should lead to a gradual weakening through day 5. The NHC intensity forecast continues to be a blend of the SHIPS and LGEM guidance, which have performed better than the dynamical guidance with Jimena's strengthening. As was noted earlier today, once Jimena reaches its peak as a major hurricane, fluctuations in intensity that deviate from the official forecast are likely due to possible eyewall replacements. Jimena is still moving westward, or 270/10 kt. The strong deep-layer ridge to the north of the hurricane is expected to weaken within 24 hours, which should allow Jimena to turn west-northwestward by this time tomorrow. This trajectory should then continue through day 5. The track guidance remains tightly clustered, although the GFS and the ECMWF shifted a bit northeastward on this cycle and lie near the edge of the guidance envelope. Due to this shift, the new NHC track forecast lies slightly right of and a little slower than the previous forecast through 48 hours. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 12.3N 123.1W 90 KT 105 MPH 12H 29/0600Z 12.4N 124.4W 100 KT 115 MPH 24H 29/1800Z 12.9N 126.2W 115 KT 130 MPH 36H 30/0600Z 13.7N 128.1W 125 KT 145 MPH 48H 30/1800Z 14.6N 130.3W 125 KT 145 MPH 72H 31/1800Z 16.2N 135.1W 120 KT 140 MPH 96H 01/1800Z 17.2N 138.7W 105 KT 120 MPH 120H 02/1800Z 17.7N 140.7W 90 KT 105 MPH $$ Forecaster Berg

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