Why am I getting an error saying a JSON object cannot be converted to string?

package com.dredaydesigns.stormy;

import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.widget.Toast;

import com.squareup.okhttp.Call;
import com.squareup.okhttp.Callback;
import com.squareup.okhttp.OkHttpClient;
import com.squareup.okhttp.Request;
import com.squareup.okhttp.Response;

import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;

public class MainActivity extends ActionBarActivity {
    public static final String TAG = MainActivity.class.getSimpleName();
    private CurrentWeather mCurrentWeather;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        String apiKey = "27974c4bc33201748eaf542a6769c3b7";
        double latitude = 37.8267;
        double longitude = -122.423;
        String forecastUrl = "https://api.forecast.io/forecast/" + apiKey +
                "/" + latitude + "," + longitude;

        if (isNetworkAvailable()) {


            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    .url(forecastUrl)
                    .build();

            Call call = client.newCall(request);
            call.enqueue(new Callback() {
                @Override
                public void onFailure(Request request, IOException e) {

                }

                @Override
                public void onResponse(Response response) throws IOException {
                    try {
                        String jsonData = response.body().string();
                        if (response.isSuccessful()) {
                            Log.v(TAG, jsonData);
                                mCurrentWeather = getCurrentDetails(jsonData);
                        } else {
                            alertUserAboutError();
                        }
                    } catch (IOException e) {
                        Log.e(TAG, "Exception caught: ", e);
                                               }
                    catch (JSONException e) {
                        Log.e(TAG, "Exception caught: ", e);
                    }
                }
            });
        }
            else {
                Toast.makeText(this, getString(R.string.networkunavailablemessage),
                Toast.LENGTH_LONG).show();

        }
            Log.d(TAG, "Main UI code is running.");
    }

    private CurrentWeather getCurrentDetails(String jsonData) throws JSONException {
        JSONObject forecast = new JSONObject(jsonData);
        String timezone = forecast.getString("timezone");
        Log.i(TAG, "From JSON:" + timezone);

        JSONObject currently = forecast.getJSONObject(currently);

                CurrentWeather currentWeather = new CurrentWeather();
                currentWeather.setHumidity(currently.getDouble("humidity"));
                currentWeather.setTime(currently.getLong("time"));
                currentWeather.setIcon(currently.getString("icon"));
                currentWeather.setPrecipChance(currently.getDouble("precipProbability"));
                currentWeather.setTemperature(currently.getDouble("temperature"));


        return currentWeather;
    }

    private boolean isNetworkAvailable() {
        ConnectivityManager manager = (ConnectivityManager)
                getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = manager.getActiveNetworkInfo();
        boolean isAvailable = false;
        if (networkInfo!= null && networkInfo.isConnected()){
            isAvailable = true;
        }
        return isAvailable;
    }

    private void alertUserAboutError() {
        AlertDialogFragment dialog = new AlertDialogFragment();
        dialog.show(getFragmentManager(), "error_dialog");

    }


}