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Tropical Storm ISELLE Forecast Discussion Number 3

2014-08-01 10:48:41| National Hurricane Center (East Pacific)

Issued at 200 AM PDT FRI AUG 01 2014 000 WTPZ44 KNHC 010848 TCDEP4 TROPICAL STORM ISELLE DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 AM PDT FRI AUG 01 2014 Iselle is continuing on an intensification trend with very deep convection in a central dense overcast feature. A recent AMSU microwave pass also suggests that the inner core has become better defined, with perhaps a partial eyewall in the eastern semicircle. The initial wind speed is raised to 50 kt based on an ASCAT-B pass from 0507 UTC. Environmental conditions appear conducive for further strengthening over the next couple of days with light-to-moderate northeasterly shear and warm water. Although the SHIPS-RI index has decreased somewhat from the last cycle, rapid intensification remains a possibility, especially given the recent development of inner core features. The NHC forecast is raised from the previous one, on the higher side of the guidance envelope close to the SHIPS and FSSE models. After 48 hours, Iselle should be moving into a more stable environment near cooler SSTs. Thus, a gradual weakening is forecast, near or slightly above the intensity consensus. Iselle continues to move to the west-northwest while it remains to the south of the subtropical ridge. Global models are in excellent agreement on this general track for the next 3 days while the ridge persists. After that time, the track uncertainty greatly increases due to a trough digging into the eastern Pacific, near or east of the forecast longitude of Iselle. With many varying solutions from the global models, it makes sense to stay close to the track consensus, which generally moves Iselle westward at long range. Since this consensus is near the last NHC prediction, the new forecast is basically unchanged from 6 hours ago. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 13.5N 124.6W 50 KT 60 MPH 12H 01/1800Z 14.1N 125.9W 60 KT 70 MPH 24H 02/0600Z 14.8N 127.6W 70 KT 80 MPH 36H 02/1800Z 15.3N 129.4W 75 KT 85 MPH 48H 03/0600Z 15.8N 131.3W 75 KT 85 MPH 72H 04/0600Z 16.5N 134.8W 70 KT 80 MPH 96H 05/0600Z 16.8N 137.5W 60 KT 70 MPH 120H 06/0600Z 17.0N 140.5W 50 KT 60 MPH $$ Forecaster Blake

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Tropical Storm BERTHA Forecast Discussion Number 2

2014-08-01 10:48:09| National Hurricane Center (Atlantic)

Issued at 500 AM AST FRI AUG 01 2014 000 WTNT43 KNHC 010847 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 500 AM AST FRI AUG 01 2014 Bertha is a sheared tropical cyclone with the center located on the western edge of the deep convection as indicated by satellite. The low-level circulation continues to be vigorous, but given the current westerly shear the outflow is very limited. There are no reasons to change the initial intensity which is kept at 40 knots. Another Air Force reconnaissance plane will investigate Bertha in the next several hours. The current shear environment is not particularly favorable for strengthening, but there are some indications by the global models that the shear could decrease some as Bertha moves across the northeastern Caribbean Sea. This should allow some slight intensification during the next 24 to 36 hours. Once Bertha's circulation moves away from Hispaniola beyond 48 hours, there is an opportunity for additional strengthening if the shear becomes lighter as suggested by global and statistical models. At this time, the NHC forecast keeps Bertha with 45-knot winds over the western Atlantic until it becomes more certain that the shear could subside. Bertha continues racing toward the west-northwest or 290 degrees at 17 knots. The cyclone is being steered by the flow around the Atlantic subtropical ridge which is forecast to persist. Once in the western Atlantic near the eastern Bahamas, Bertha will be steered by the southerly flow between the subtropical high and a mid-level trough over the eastern United States. This pattern will force Bertha to turn northward with a decrease in forward speed and to eventually recurve northeastward over the Atlantic. The confidence in the track forecast, primarily in the next 2 to 3 days, is high since most the guidance is tightly clustered. The confidence decreases after 3 days when the guidance becomes divergent. The track envelope, however, brings Bertha northward and then northeastward over the Atlantic, and the NHC forecast follows closely the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 13.0N 57.0W 40 KT 45 MPH 12H 01/1800Z 14.0N 59.6W 40 KT 45 MPH 24H 02/0600Z 15.5N 63.0W 40 KT 45 MPH 36H 02/1800Z 17.2N 66.0W 45 KT 50 MPH 48H 03/0600Z 19.5N 68.8W 45 KT 50 MPH 72H 04/0600Z 24.5N 73.5W 45 KT 50 MPH 96H 05/0600Z 29.0N 74.0W 45 KT 50 MPH 120H 06/0600Z 35.0N 67.5W 45 KT 50 MPH $$ Forecaster Avila

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Tropical Storm BERTHA Forecast Discussion Number 1

2014-08-01 05:21:43| National Hurricane Center (Atlantic)

Issued at 1100 PM AST THU JUL 31 2014 000 WTNT43 KNHC 010321 TCDAT3 TROPICAL STORM BERTHA DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032014 1100 PM AST THU JUL 31 2014 Reports from an Air Force Reserve reconnaissance aircraft earlier this afternoon and evening indicated that the well-defined low pressure system located about 250 nmi east-southeast of Barbados had surface winds of about 40 kt north and northeast of the center. Since the departure of the aircraft, a band of deep convection has developed near and to the north and east of the low-level center, and now has enough organization to consider this system a tropical cyclone. The initial motion estimate is 290/17 kt. Bertha is moving along the southern periphery of a strong subtropical ridge located to the north based on earlier dropsonde data obtained by a NOAA Gulfstream-IV jet aircraft. The NHC model guidance is in excellent agreement on the cyclone maintaining a general west-northwestward motion for the next 48 hours or so, followed by a gradual turn toward the northwest after that through 96 hours. By Day 5, Bertha is expected to turn northward as it moves around the western portion of the ridge. The official forecast track is similar to but slightly north of the consensus model, TVCA. The environment surrounding Bertha is not particularly favorable for significant strengthening during the next two days due to modest westerly shear and limited mid-level moisture. However, the cyclone will be moving over increasing SSTs and within an upper-level atmosphere that is slightly cooler than normal. The resultant increase in instability could allow for some slight strengthening to occur before Bertha interacts with Puerto Rico and eastern Hispaniola in about 48 hours or so. After the cyclone clears land, some slight re-strengthening is possible based on the SHIPS model indicating that the vertical shear decreasing to less than 10 kt and SSTs increasing to near 29C. The NHC intensity forecast is similar to the consensus model ICON. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 12.3N 55.5W 40 KT 45 MPH 12H 01/1200Z 13.2N 58.0W 40 KT 45 MPH 24H 02/0000Z 14.5N 61.4W 40 KT 45 MPH 36H 02/1200Z 16.1N 64.7W 45 KT 50 MPH 48H 03/0000Z 17.9N 67.9W 45 KT 50 MPH 72H 04/0000Z 22.0N 73.0W 35 KT 40 MPH 96H 05/0000Z 26.8N 75.2W 40 KT 45 MPH 120H 06/0000Z 32.0N 74.7W 45 KT 50 MPH $$ Forecaster Stewart

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Tropical Storm ISELLE Forecast Discussion Number 2

2014-08-01 04:26:38| National Hurricane Center (East Pacific)

Issued at 800 PM PDT THU JUL 31 2014 000 WTPZ44 KNHC 010226 TCDEP4 TROPICAL STORM ISELLE DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 PM PDT THU JUL 31 2014 The satellite presentation of Iselle features an area of cold convective tops mainly to the north and east of the estimated center position, and the poleward outflow has been enhanced somewhat due to an upper-level trough to the northwest. The initial intensity has been raised to 40 kt based on a blend of the TAFB Dvorak estimate and the latest ADT from UW-CIMSS. Conditions appear favorable for steady intensification during the next couple of days. In fact, rapid strengthening is a possibility during the next 24 hours with the SHIPS RI index showing a 40 percent chance of a 25-kt increase in the next 24 hours. After 72 hours SSTs cool somewhat along the forecast track, which should result in gradual weakening. The NHC intensity forecast has been adjusted upward a little from the previous advisory and is close to or just below the SHIPS model through the period and above the intensity consensus. The initial motion estimate is a somewhat uncertain 290/10 given the recent formation of the cyclone, and the initial position is a little to the south and west of previous estimates. Overall the track forecast reasoning has not changed, as Iselle will be steered generally west-northwestward south of the subtropical ridge for the next 72 hours or so. After that time, the ridge weakens as a mid/upper-level trough digs equatorward along 135W, which should result is a slower westward motion late in the period. The track guidance envelope remains tightly clustered for the first 48 hours and the only change to the NHC track during that time is a westward adjustment due to the initial position and motion. Late in the period the spread of the guidance increases a little, and the envelope has shifted northward this cycle. At days 3 through 5 the NHC track has been adjusted northward and westward, but still lies south of the TVCE multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 13.2N 123.9W 40 KT 45 MPH 12H 01/1200Z 13.8N 125.1W 50 KT 60 MPH 24H 02/0000Z 14.6N 126.7W 60 KT 70 MPH 36H 02/1200Z 15.2N 128.3W 65 KT 75 MPH 48H 03/0000Z 15.6N 130.1W 70 KT 80 MPH 72H 04/0000Z 16.5N 134.0W 70 KT 80 MPH 96H 05/0000Z 16.5N 136.5W 60 KT 70 MPH 120H 06/0000Z 16.5N 140.0W 55 KT 65 MPH $$ Forecaster Brennan

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Tropical Storm ISELLE Forecast Discussion Number 1

2014-07-31 22:36:09| National Hurricane Center (East Pacific)

Issued at 200 PM PDT THU JUL 31 2014 000 WTPZ44 KNHC 312036 TCDEP4 TROPICAL STORM ISELLE DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 PM PDT THU JUL 31 2014 Deep convection has been wrapping up quickly during the past few hours near the low pressure system located near 122W, and TAFB and SAB have both provided Dvorak estimates of T2.0/30 kt. In addition, a partial 1800 UTC ASCAT-B pass indicated that the low is already producing winds to tropical storm force in the eastern semicircle. Therefore, advisories are being initiated on Tropical Storm Iselle, and the maximum winds are conservatively set at 35 kt. With sea surface temperatures ahead of Iselle running between 27-28C and vertical shear not expected to be a significant limiting factor, the storm is forecast to strengthen for at least the next 3 days. The strengthening rate could be quick for the next day or so, with the SHIPS rapid intensification index showing a 44 percent chance of a 25-kt increase in winds by this time tomorrow. The SHIPS guidance is the most aggressive of the intensity models and brings Iselle to hurricane status within the next 24-36 hours. The NHC official intensity forecast is not as high as the SHIPS model, but since the environment looks favorable for strengthening, it does lie a little above the intensity consensus ICON. Iselle is located to the south of a mid-level ridge which extends from northwestern Mexico southwestward to near 20N140W, and the cyclone's estimated initial motion is 295/9 kt. In general, ridging is expected to maintain a relatively steady west-northwestward motion for the next several days. Some slight decrease in forward speed is possible by day 4 when a weakness develops within the ridge near 135W and ridging strengthens near the Hawaiian Islands. The track guidance is tightly clustered for this forecast, and the NHC track forecast lies very close to the multi-model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 12.7N 122.3W 35 KT 40 MPH 12H 01/0600Z 13.4N 123.5W 45 KT 50 MPH 24H 01/1800Z 14.2N 125.0W 55 KT 65 MPH 36H 02/0600Z 14.8N 126.7W 60 KT 70 MPH 48H 02/1800Z 15.1N 128.3W 65 KT 75 MPH 72H 03/1800Z 16.0N 132.0W 70 KT 80 MPH 96H 04/1800Z 16.0N 135.0W 65 KT 75 MPH 120H 05/1800Z 16.0N 138.0W 60 KT 70 MPH $$ Forecaster Berg

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